/SQT/ - Stupid Question Thread

[Anonymous No.7997244]

Don't make a thread with your question as the OP because we all know you do it so people might answer your question - edition.

Ask questions here like
>silly HW questions
>concepts or things you might not understand
>dumb little short questions that probably wouldn't be a good OP but still worth asking

[Anonymous No.7997278]

Explain the Lorentz transformations to a retard please. I only got the [math](t_{2}-t_{1})^2 - (x_{2}-x_{1})^2 - (y_{2}-y_{1})^2 - (z_{2}-z_{1})^2 = 0[/math] part, and the time dilation via multiplication by the Lorentz factor. I don't get the rest.

[Anonymous No.7997295]

>>7997278
Since you don't measure absolute velocities, only velocities relative to your reference frame, you need a way of transforming between the different frame's. Otherwise you'd end up in the bizarre situation where physics was affected by the velocity of your frame. Classically we the Galilean transformation (which if you've never heard of before might help you). When we get to relativistic velocities we find the Galilean transformation no linger works (it predicts that the speed of light should be dependent on the frame velocity when we know from both theory and experiment that it's a constant in all frames). So we need a relativistic generalisation of the classical transform, that lead's us to the Lorentz transformation. Better?

[Anonymous No.7997315]

>>7997295
I get that, but what I don't get is the math behind the transformations, and how to get from the classical Galilean transformation to a relativistic one.

[Anonymous No.7997330]

somebody explain like I'm 12 the fundamental theorem of calculus

[Anonymous No.7997332]

>>7997315
>I don't get is the math behind the transformations
What don't you get?

>how to get from the classical Galilean transformation to a relativistic one.
Well here's the thing, you don't go from classical to relativistic. Part of its derivation includes an appeal to the "correspondence principal" which means that at low velocities you return the classical transform. Einstein's original paper is called "On the electrodynamics of moving bodies" you might gain something by reading it.

[Anonymous No.7997334]

>>7997330
The integral of f from a to b is the same as the antiderivative of f at b minus the antiderivative at a

[Anonymous No.7997343]

>>7997334
Doesn't really explain anything about the fundamental theorem of calculus. What is the idea/theory behind it? I know how to evaluate a definite integral already.

[Anonymous No.7997346]

>>7997332
The part that I don't get is how to get from general linear transformations to Lorentz transformations.

[Anonymous No.7997348]

>>7997343
Have you constructed an integral via riemann, darboux, Stieltjes or lebesgue?

[Anonymous No.7997353]

>>7997348
I know Riemann.

[Anonymous No.7997358]

>>7997330
average rate of change × interval = area

[Anonymous No.7997359]

>>7997343
Basically, an integral between two points of a function is the net area under the curve of that function. That is, the area above the curve minus the area under the curve. This area represents the net change of the value of the function between these two points.
The value of the function will depend on the net change. The more the net change is, the higher the value.

This is as "intuitive" as I can get. You should probably watch a video by KhanAcademy, he explains it better.

[Anonymous No.7997362]

>>7997353
Well thats the FTC. That the inverse of the derivative is the integral and vice versa.
Slopes and areas dude. They're related

[Anonymous No.7997366]

Is IQ meaningful? And could someone link studies supporting their answer?

[Anonymous No.7997370]

>>7997362
>>7997359
Much appreciated!

[Anonymous No.7997401]

>>7997343
The general idea is this - final minus initial.

Now i know you might be thinking "well duh" but you kinda gotta look at a proof of it to understand. That is what I would recommend first.

The general idea is this though - let's consider an integration over this region from 0. We know that base times height gives us the area of it. So since it starts from the origin, we can do that calculation pretty easily.

Now consider a triangle. We know the equation for that. But what if it didn't start at the origin? Well we could still find the base measurement by taking the final x coordinate minus the initial x coordinate.

Well as it turns out, integration is the same as finding the area of a surface. That's what the FTC is capitalizing on - you can simplify almost any figure into a base times height problem.

Now what goes on in the background of this is KIND OF black magic and I admit it myself. But I think a triangle is a pretty good way to see what is happening. Take a function x, which is the slope of a triangle. (duh) the integral of that is what we recognize as the area of the triangle. We know that works obviously and we talked about the final minus initial method for the measurements. Right? You'll find that if you just keep coming up with functions that have a shape, integrating over them gives you the simple area equation you know and love. (go ahead and see if you want)

So, it's what happens in between that is black magic. It turns out that when you do this, you are taking an infinite amount of slivers underneath your function, and when you take final minus initial, math (again, you need to look up a proof for this I imagine) works in a way that you are taking all those slivers and adding the area of said slivers to get an area. It's kind of neat.

Don't know if this helps since I don't know why you are hung up on it, but

[Anonymous No.7997433]

>>7997330
If f(t) is distance at time t, f'(t) is velocity at time t.
At small time intervals I, [math] f'(t)|I|[/math] is roughly the distance you cover in the interval I.
If you chop the interval [a,b] into infinite infinitesimally small subintervals [math] I_k[/math] and sum you get the total distance covered [math] f(b)-f(a)[/math]

[Anonymous No.7997488]

What are some good physics resources to learn? I'm taking calculus based physics 1 right now, and its not too bad but I feel like I could be learning it much better. I was not impressed with the Khan Academy videos

[Anonymous No.7997534]

Just stepped outside, and I got hit by the strong scent of rotten eggs. Can't figure out where it's coming from, could it have anything to do with the thunderstorm outside?

[Anonymous No.7997602]

>>7997346
Like the other guy said, you don't go from a simple linear transform to a Lorentz transform. The Lorentz transform is gained from a ground up derivation with extra conditions. The regular Galilean transform is an approximation of the Lorentz transform at velocities much lower than c.

[Anonymous No.7997629]

Anyone? >>7997366

[Anonymous No.7997634]

>>7997629
It's a good indicator of how good you are at IQ tests

[Anonymous No.7997931]

Working on practice exams for a diffy exam I have, and something came up that has me a little bothered.

"For what range of b will the solution to the differential equation oscillate indefinitely?

y'' - by' +(2b - 3)y = 0

I was under the impression that since this is a damped system, it would never oscillate indefinitely, but solutions list it as the range from 2 to 6. (IE, the range of which underdamped motion)

Do I not have this correct? Or is something botched? If it's underdamped motion, shouldn't it just gradually decrease to zero?

[Anonymous No.7997997]

can I borrow one of you math autist for a quick 30 question pre calc quiz?

>inb4 learn it brainlet
I am trying but I fell behind the first couple weeks due to moving right when the term started. Plz halp

[Anonymous No.7998011]

>>7997330
The idea is that you have some function, say x^2

You'd like to know the area of x^2 for whatever reason. You pick two arbitrary points on the function, say from 0 - 1. From here you take the anti derivative of the function so (x^3)/3 +C and plug in your values so you get 1/3 - 0.

To make it even simpler think of final - initial.

>>7997534
Ozone

[Anonymous No.7998013]

>>7997244
So if I write a program what exactly is happening on the hardware? Are the circuits just opening in closing in a specific fashion?

I remember when I took comp sci 101 they told me that the compiler makes the program as small as possible, sends the instructions to the CPU and then executes them in the order it was sent.

[Anonymous No.7998060]

I don't get how to add / subtract trig functions.

How would you do this for example:
csc 30° - cos 45°

[Anonymous No.7998275]

Really dumb question,

But determining "if a is a primitive root modulo m"

means just checking if it is a primitive root right?

[Anonymous No.7998286]

Eff man came from monkeys, y r their still munkeys?

[Anonymous No.7998300]

>>7998013
Imagine a lighthouse overlooking a bay and a ship out at the sea. The ship is trying to navigate, and the operator of the lighthouse sits inside the lighthouse. The operator is at his desk on his computer, using a computer, which runs programs. That's how computers run programs.

>>7998060
Use trigonometry

>>7998275
I don't know

>>7998286
Because the set containing the zero vector has dimension zero

[Anonymous No.7998303]

>>7998060
0, 30, 45, 60, 90 degrees are special angles and you should memorize the values of sin and cos at each of them. Then evaluating that is easy.

>>7998275
You're checking if the order of a is phi(m).

[Anonymous No.7998306]

>>7998060
Switch to rational trig and then just substitute and solve

[Anonymous No.7998308]

>>7998013
I took a great class called digital design that explained how to get from logic gates to basic computers.

Then all you need is to understand assembly and you'll have a decent understanding down to the transistor level.

I wish I could tell you more but I'd have to reread the book

[Anonymous No.7998321]

>>7997534
Rotten eggs smell is hydrogen sulfide.
common sources are volcanic springs, flatulance and rotten eggs, but Ive had water that had the taste.

I have no idea why it could come from rain, unless you have acid rain coming down and it somehow broke down.
The only sulfuric acid I've smelled smelled like burning nose.

>>7998011
Ozone smells like sparks

[Anonymous No.7998325]

>>7997931
Effectively it damps out, but technically it keeps overshooting the final value for all eternity.
In control theory we use something called a settling time where we see how long it takes to get to a percentage of that final value (usually 98% iirc) and the only system that would oscillate forever is the undamped one.

[Anonymous No.7998475]

I'm not very smart and I can't figure out how to word it properly on google to get the results, but something that's always bothered me is that on one hand, people bring up that we can't see past the edge of the observable universe, but on the other hand, people say that we can see the beginning of the universe.

How exactly does that work? How can we see both the end of the observable universe(the point which we can't see any further) and also the beginning?

[Anonymous No.7998484]

>>7998475
The end of the universe is the beginning!!

Now for the less fun stuff:
Light takes time to travel to us, so we can see in the past by looking out at something at a distance.
Farther we look, earlier in the past.
The observable universe is everything we can see (duh) so theres no possibility of seeing past it. Since its the furthest part it must be the oldest.
The reason we can't see past the edge of the observable universe is because there was no before it. So there's no photons that have reached us from past that boundary

Bonus: things are expanding away at a faster and faster rate. If a point is expanding away from us at a speed over the speed of light, there's no way for it to interact with us.

[Anonymous No.7998508]

>>7997931
Use the determinant after y=e^Mt
Any range of b greater than 0 oscillates indefinitely

[Anonymous No.7998527]

>>7997244
I'm not understanding what this question asks me so if any of you could help my deconstruct it that would be great.
Background info: Deep space probes such as Voyager, are powered by “thermionic” devices which convert the heat from radioactive decay directly into electrical energy. The typical radioisotopes used is 238 Pu 94 which decays via alpha emission to 234 U 92.

Pu-238 = 238.0495 u U-234 = 234.0409 u He-4 = 4.0026 u

The question is: If all the energy comes from the kinetic energy of the alpha decay, calculate the number of decays in 1 second, if the activity of the Plutonium is 1.45 x 10 14 Bq.

[Anonymous No.7998543]

This is my answer to one of the dumb ass questions on OKCupid. Did I do alright?

[Anonymous No.7998548]

>>7998543
This is pretty simple and I'd hope the average person could understand it. Not sure if this was an attempt at "bragging", but this seems incredibly autistic that you would even do that.

[Anonymous No.7998549]

>>7998548
The main reason I did it is because I am in Sequences and Series calculus right now and was working on homework with these exact types of problems.

So yes I am partially bragging and also displaying my autism for all to see to see if it attracts any ladies

[Anonymous No.7998850]

Would it be possible to create a formula, that can solve every math problem by having variables that have a value belonging just to the problem you are about to solve?

[Anonymous No.7998862]

Anyone has a good guide on how to design a tube and shell heat exchanger? I'm interested in reviewing how to design one.

[Anonymous No.7999096]

>>7998325
>>7998508
Okay, good stuff. Cheers anons,

[Anonymous No.7999102]

>>7998862
you can do back of the napkin design with just an undergraduate heat transfer text. however you would probably have to adjust final flow rates.

if you want some on-the-nuts design, your gonna have to fire up Solidworks or Fluent and do a simulation.

[Anonymous No.7999343]

If t=x/(x+1), why is (x+1)/x=1/t?

[Anonymous No.7999417]

Good purchase?

[Anonymous No.7999421]

>>7999417
Only bought the quick calculus shit because I need to be able to solve baby calculus problems easily for now, after I take that exam I will study calculus profoundly from a real book.
Also, studying number theory from Serge Lang's basic math.

[Anonymous No.7999427]

Given a 90% confidence interval, how do I find the sample standard deviation? I'm not given n, so I'm not sure how to go about this.

[Anonymous No.7999450]

>>7999427

Okay so I divided the two bounds by each other so I got the ratios of the chi-squared values, each of df n-1. I suppose I'm meant to test out different ratios from my table corresponding to the 90% interval until I find this particular one.

[Anonymous No.7999464]

>>7999450

Well that ended up working after a few tries, thanks /sci/

[Anonymous No.7999475]

>>7997244
Are there any good resources that could teach me how to determine the solubility of elements or compounds in molten metals versus solid state metal?

I want to understand Zone Refining better.

[Anonymous No.7999652]

I'm sorry for being so stupid, but why does
[math]r_a -r_b[/math] being a multiple of m implies that [math]-m<r_a-r_b<m[/math] here?

[Anonymous No.7999685]

>>7999652

Because if I'm interpreting the image correctly, then this is part of a demonstration of some division/Euclidian algorithm, or similar which I should know OTTOMH but don't. In other words, each individual letter-form stands for some natural number, and since thingy is a multiple of m, oh dear now I've gone cross-eyed and and the things contradict my above assumptions.

So we really need more context. In fact, we need the context of the larger train of thought to make sense of this. It's obviously moving along toward some other step, but we don't know what. Given my above assumptions, perhaps a (proof by) contradiction is in the offing, but again we don't know without more information.

The "OTOH" clause suggests that the author is aware of putting two conflicting pieces of information side-by-side, which goes to my above supposition.

[Anonymous No.7999702]

>>7999685
Oh damn, I seriously am retarded, I didn't even think about that. Here's the context.
I'm really sorry, I'm trying to understand this proof through.

[Anonymous No.7999734]

Why do roboticists insist on building fuck-ugly rubber zombies that no one without autism could ever find beautiful, elegant, attractive, or aesthetically pleasing?

[Anonymous No.7999744]

>>7999734
They're desperate for investors and they don't think they can get any with faggy cartoon shit

[Anonymous No.7999754]

>>7999702
If you look at the first page, 0<=ra<m and 0<=rb<m. ra and rb are both positive and less than m, so think about it. if ra>rb then ra-rb will be positive (but still less then m because they are both less than m). if rb>ra then ra-rb is a negative number but for the same reason as before its gonna be larger than -m. I didn't read the whole proof, I'm just answering your original question.

[Anonymous No.7999766]

>>7999754
Wow, that was really helpful. I get it know, my question was answered. Thanks a lot.

[Anonymous No.7999777]

>>7999744
Because nasty uncanny valley monsters are working SO well for them.

[Anonymous No.7999847]

>>7999702

And so my above assumptions were mostly correct (division argument and only integers) and the author is not driving toward a contradiction as such, but rather a simple forcing that "thingy" can only be equal to zero, which [he] then uses to establish his other thingy (his theorem, which I would instead call a lemma, doesn't matter).

Because both "r" remainders are manifestly natural numbers. And their difference is T, or "thingy". Maybe T is even a negative number, for all I know. But it definitely isn't greater than or equal to m. Because neither one is. If you were adding the two, it might be a different story. But we're not, so it isn't.

The one train thought shows that m | T. That is, m divides T. T is a multiple of m. But also, since neither one of the remainders is equal to or greater than m (which is just a natural number) then no matter how you slice it, T is strictly less than m.

So we have two conditions, where m is some natural number (inclusive of zero, read the above), and T is some integer (maybe it's negative!). The two conditions are, that

T < m

and there exists some other integer U such that

Um = T

All three of those things are integers, when you really look at it, there's just a restriction on m. If m is zero, then T is zero. And we don't care what integer U is, it could be anything. And if m is one, then U = T < 1. So T is AT MOST equal to zero, but along my alternate route, I hold open the possibility that T is some negative number.

How about when m is two, or anything greater? Well then it gets multiplied by some other integer and it ends up being less than m (since T < m). And the only way for that to happen, is if U is non-positive.

The point is that in one case I thought about (the cases here, are the choices of m), T was forced to be zero, and nothing else. And in the other two cases, zero remains open as a possibility. I leave the rest to you as an exercise to understand (hint: -m is a lower bound, too)

[Anonymous No.7999849]

Can someone explain to me what the flaw in this logic is? I know it can't be correct, right?

[Anonymous No.7999856]

>>7999849
Because there's no such thing as a square root of a negative number, unless it's an imaginary number. And then, it becomes an entirely different story.
In other words, learn what imaginary numbers are.

[Anonymous No.7999862]

>>7999856
I'm not super great at math, but I know what imaginary numbers are, and when shown the problem I just did (2i)(3i) = -6

I was shown this solution and I don't understand why doing it this way is flawed.

[Anonymous No.7999874]

>>7999744

the VR goggles seem to be taking care of the faggy cartoon shit for the moment. Or what amounts to the same thing, hentai on the internet.

[Anonymous No.7999876]

What books are considered to be Math Classics/Must reads? Books like, for instance, Principia Mathematica or Elements by Euclid? If possible, what order to read them?

[Anonymous No.7999910]

>>7999862

When you took the square root in step 4, you introduced the possibility of two solutions to the intermediate equation 36 = x^2. Because you've been taught to do this by rote when taking a square root.

But in your first line, you had specified that x has exactly one value (among the complex numbers), and not two. So in a sense you're "starting" from two different points, which is where part of your confusion is.

The LHS (left hand side) of your first line has a unique, unambiguous interpretation among complex numbers. The two bits become (2i)(3i), which only simplifies to -6, and not to 6. If we had wanted to indicate the negative (opposite) of either of those bits, we would have instead written something like -√-4 instead, which is our convention to avoid ambiguity. It is possible that you were not aware of this convention, either, which would contribute to your confusion.

The radical sign, used together with other symbols, is used to denote unique complex numbers, according to a given convention. But the act of taking a square root (and not just pushing radical signs/symbols around) does introduce the possibility of two roots. But in a mathematical argument, one has to keep track of, and consider every step. Your conclusion is false because you're confusing the two usages. Your original LHS is only, exactly equal to -6, by our conventional notation. to get +6, simply put a negative sign in front of either radical, and bracket as necessary to avoid further confusion.

[Anonymous No.7999912]

>>7999862
I'll make it simple. If A = B, then A^2 = B^2, but the reciprocal isn't true. With a simpler example you'll see:

x = -3
x^2 = 9
x = +/- 3

But only one value of x is correct.

> tl dr: Squaring an equation may induce incorrect solutions, you have to check them in the original.

> There is nothing fundamentally wrong working with sqrt(-4) in the pure algebraic sense (the number whose square is -4) and making algebraic manipulations with it. But remember it's not uniquely defined (assignation of i or -i is arbitrary) and you shouldn't drag this habit when operating with functions.

[Anonymous No.7999920]

>>7997244
psych question

Various tests have labelled me as having sociopathic tendencies. No friends, apathetic, sardonic.. etc

however, in my neuroscience class I took a test recognizing microexpressions, and got a perfect score, twice.

Doesn't empathy and sociopathy contradict?
Does having low empathy cause someone to be more analytical?

To clarify, I'm using the word sociopathy seperate from psychopathy. Psycho being, emotional part of brain doesn’t light up. Socio being a dull or suppressed signal.

[Anonymous No.7999930]

>>7999849
[math](\sqrt{-4}\sqrt{-9})^2 \ne 36[/math]

[Anonymous No.7999933]

>>7999912
>>7999910
Awesome thanks a lot guys, that really cleared it up

[Anonymous No.7999937]

How do astronauts fap?

Can you get a boner in zero G?

[Anonymous No.7999939]

Is IQ meaningful? And could someone link studies supporting their answer?

[Anonymous No.7999940]

>>7999930
Your complex analysis teacher will congratulate you for your rigor and accurate understanding.

Your field theory teacher will fail you immediately after seeing you can't handle a simple algebraic operation in a field.

[Anonymous No.7999976]

Why is computer science the best science?

[Anonymous No.7999979]

>>7999976
Because it can simulate all other sciences.

[Anonymous No.8000025]

>>7999876

Mathematics has developed very rapidly in about the past 200 years or so. So much so in fact, that texts become obsolete or irrelevant quite rapidly. This is why /sci/ discussion of reading material focuses on textbooks and not "original works". What true /sci/entists and mathematicians, etc, are interested in is less history, and more about whatever is relevant to their area, expositing it in a clear and up-to-date fashion. A math grad student is not (ordinarily) going to read Ars Magna, /either Principia/, or the Rhind Papyrus to get any worthwhile insight into modern mathematics, into his own area.

However having said that, if someone has an interest, then they will at certain times be interested in the history of what interests them. Historical interest is the main reason to read old math, and not deep mathematical insight of itself. I will assume that you share this interest with me, since I concentrated on both history and math in college.

cont.

[Anonymous No.8000030]

>>8000025

The major exception to the above is Euclid's elements, yes, so I recommend that first of all. Look up some demonstrations online, be prepared to look up words elsewhere online, and decide if you want to continue and actually work on it. It is both a historically valuable text, and an ancient message of /properly/ mathematical (if simple) argument. People have been known to /complain/ about Euclid on this board; they understand neither history, nor math. I cannot overstate the next sentence. /We are still doing mathematics in the same way that Euclid did mathematics./ What do I mean by this? Obviously I'm not referring to the fields and tricks that we have now - we have a lot more of those now, the ahistorian will boast. Euclid is a meme, fuck Euclid, he might say. But I've pre-empted him about the latest, sexiest fields.

What did Euclid /do/? He thought carefully, experimented, thought some more, built on what others had done, drafted, edited, hazarded a few completely reasonable assumptions, and from those, derived diverse results, /using abstract chains of reasoning, which he then wrote down/. He /used/ certain results to build /even more, interesting results/. He then /organized/ what he had done. Even the way that the /page/ looks is fundamentally the same as what we prepare today: a page, mostly text, also punctuated with formulas and the periodic diagram. Regarding abstract thought on measurements, quantities, signifiers, and their relationships. The activity I'm describing sounds an awful lot like the routine in a profession that I can think of.

There is a reason why Euclid was actually used as a math textbook up until about a century ago. The vocabulary has changed and we've gotten into sexy algebraic geometry and IUT and so on, but Euclid's intellectual activity and creative work are fundamentally the same thing that we do today. That part hasn't changed. That part has stayed the same.

Euclid is not a meme. Euclid was the real deal.

[Anonymous No.8000036]

>>8000030

[Anonymous No.8000056]

>>8000025
>>8000030
Thanks bro, appreciate your reply

[Anonymous No.8000227]

>>7999876

Continuing with the above, the Elements is a solid "math classic". Let's talk about some other historic texts, along these lines.

First of all, just to make it clear, there are two texts called "Principia Mathematica". The first is the physics text by Newton, and the second is the early 20th century work by Whitehead and Russell, on foundations of mathematics. You absolutely do NOT need to read the latter, its notation is atrocious, and it was largely BTFO and criticized by Godel and Wittgenstein, respectively. It is one of those "obsolete" books that I mentioned earlier, studied now mostly as a historical curiosity (because it does get mentioned a lot due to the history around it), as I said. If you really really really like physics, you might read an annotated version of the Newton text, but again, this is not a way to learn physics for the first time-we have textbooks for that.

Many people seem to like Polya-How to Solve It, so I'll suggest that one, it's not long but I haven't read it. For aesthetics, there's "A Mathematician's Apology" by Hardy, where he defends pursuing pure math for its own sake, giving his own opinion on things. This attitude causes many on /sci/ to cringe, but the latter is also quite short, and then you've read "a historic document" about /why/ people do math. And you get his version of things so then you can decide for yourself how you feel about it.

Some technical articles (actual math/logic) which are fairly short and historically important are Godel's incompleteness proofs, and Riemann's "On the number of primes less than a given magnitude". You can get cheap copies of these through Dover if you know where to look.

Apart from these, it's whatever textbooks are good, and /sci/ has threads on that topic regularly.

[Anonymous No.8000245]

What is the matter inside a black hole like? I know neutron stars merge protons and electrons into a dense lattice of neutrons. Increase the gravity and then the actual particles never seem to be talked about

[Anonymous No.8000265]

I've been looking at textbook examples of showing that something is a subspace but they all seem to lack definitiveness.
For example with showing that the set is closed under addition, they merely do the addition and then state that the result is in the right form.
For example the set of matrices
[eqn]\begin{matrix} x & x+y \\ x-y & y\end{matrix}[/eqn]
under addition becomes
[eqn]\begin{matrix} x_1+x_2 & (x_1+x_2)+(y_1+y_2) \\ (x_1+x_2)-(y_1+y_2) & y_1+y_2\end{matrix}[/eqn]
Intuitively I can see how they are in the right form, but is that enough to show that the set is closed under addition? Just associating the variables?

[Anonymous No.8000361]

>>8000265
You need to show that adding two elements of a set gives you an element of the same set, which is exactly what you've done. This is completely rigorous. It just so happens that membership in your set is determined by a matrix having entries of a certain form.

[Anonymous No.8000368]

You know how the model of the atom has changed over the decades?

What are some thoughts or ideas for future modifications to the current model of the atom?

[Anonymous No.8000375]

>>8000227
Thanks again, very helpful!

[Anonymous No.8000381]

>>8000361
Beautiful. Thanks a lot anon.

[Anonymous No.8000423]

>>7997244
I'm trying to create a recursive descent parser. So far I have all the foundation set, I just need to properly implement a few functions to enforce the grammar. I thought everything was right, it looks it, but I guess my Aop, Expr, or Term function is doing something wrong. Sometimes the input stream gets cut off and things aren't recognized. I don't see how though.

Is there any site or source that explains this more in depth, with code examples? Everything I've seen is very generic, which is fine, but I'm stuck on implementation.

I've searched the web near and far, and have not found any examples that helped me understand this; pls halp.

Here's the Expr Function [:::](http://pastebin.com/fzjcugme (embed))

This is the grammar : [Grammar](http://imgur.com/OrBnpEk))

Here's the main program with all functions. [Program](http://pastebin.com/qMB8h8vE (embed))

Please God, someone, anyone, help me. I want to see the light.

[Anonymous No.8000497]

When am I ever gonna use polar equations outside of school?

[Anonymous No.8000499]

>>8000245
Theyre trying to find stuff like pentaquarks at the LHC right now. One reason is that the inner parts of neutron stars and black holes may be super dense, exotic mesons. Its unlikely black holes will bemultiquark mesons, but understanding neutron stars always helps in furthering our understanding of their black hole cousins.

[Anonymous No.8000536]

>>7997534
Check to see if your natural gas pipes are leaking.

[Anonymous No.8000557]

>>8000497
whats your major?

[Anonymous No.8000558]

>>8000557
CS

[Anonymous No.8000569]

So I've had the fundamental theorem of calculus explained to me several times, seen formal proofs, "intuitive" explanations, watched several videos, and I still don't feel like I'm completely get it. Is this one of those things that just suddenly sort of "clicks" after a while?

[Anonymous No.8000574]

>>8000558
no. you won't use much math at all. its cool if you just brain dump everything.

[Anonymous No.8000576]

>>8000574
With an emphasis on not being a codemonkey, so likely

>Abstract algebra
>Discrete maths
>Calc I-III
>Linear Algebra

[Anonymous No.8000578]

>>8000569
i didn't really understand calculus until i took ODE's.

[Anonymous No.8000640]

>>8000499
That's actually very helpful and now I have a better understanding of what to research. Thanks

[Anonymous No.8000661]

>>7997931
This happens when for 'under damped' systems. Looks for complex roots in the characteristic equation. Open your book, or watch the MIT diffeq lectures. You might learn something.

[GooZ No.8000670]

life is vibration, energy and frequency..right? so if you mess with those things. why would you not think it would have an impact....? https://www.youtube.com/watch?v=82V6E4sm054&nohtml5=False

[Anonymous No.8000672]

>>7998543
Do sequences like this have a particular name?

[Anonymous No.8000691]

Didn't think people would like it if I tried to make a whole thread on it, and not sure how familiar /adv/ is with the subjects.

What would you guys say about my decision in double majoring in biology and mathematics? I don't want to do bionformatics or some meshed major, but as two separate ones. I love both topics a lot, and I feel by choosing one in missing out on either job opportunities or even the satisfaction of knowing both.

If it helps,!I'm trying to build a cabin and become /out/ hermit later in life, would build a home with my dad. If all goes to shit I would end up doing some comp sci stuff from home as my job to try and pay for the land. Either way I'd still be happy I knew my passions.

Criticism welcome, my question being does /sci/ think this is reasonable.

[Anonymous No.8000703]

>>7997244
http://www.ustream.tv/recorded/85314345#to01:05:31

what is this?

[Anonymous No.8000718]

>>8000691
What kind of mathematics would you want to major in? Have you been exposed to epsilon-delta proofs yet?
>and I feel by choosing one in missing out on either job opportunities
Have you done any research on the current prospects of biology undergraduates besides what the uni told you?

[Anonymous No.8000726]

>>8000691
Multiple majors are always a bad idea unless you have some scholarship paying

[Anonymous No.8000731]

>>8000569
Have you just seen formal proofs or written a formal proof for it?

[Anonymous No.8000756]

>>8000718
Still in high school, 18 year old but still a generous amount of time before I commit to any schools or majors. Not familiar with what kind of specific math I want to get into, so thanks for the heads up.

>>8000726
I guess I wasn't familiar with this, is it that much more expensive to commit to a double major? I figured I was just going to have no room for electives and maybe some extra classes on top of it but not an extraordinary amount. Money is somewhat of an issue so I'll try and research that more

[Anonymous No.8000767]

>>8000756
In my program you can double major by taking an extra semester, but that's only because some of the programs are so similar.
I think it was around $5000/semester?

Use the time you have in school to learn how to learn new things. Then just study the one you don't want the career in in your spare time.
Or switch degrees in grad school...it's often not too hard.

Talk to your advisor or dean if you don't have one yet. They'd know more about your situation/school

[Anonymous No.8000888]

>>7999876
Most math classics are not a pleasant read and with good reason. There is a reason why people hold seminars to discuss and refine proofs and theorems are often proved several.
The first time something is introduced rarely has anything to do with the way it is taught later on and a lot of expository work is usually necessary in order to make the idea intelligible (I encourage you to read some of Galois' papers to see what I am talking about).
That being said, there are still some works that might be an interesting read: Euclid's elements and Gauss' Disquisitiones (his work does not suffer from the problem that I mentionned, because he spent a notoriously long time thinking about exposition), for example.
Also, math from about a century ago is fairly readable so the original works of Poincaré, Riemann and the like are probably within reach

[Anonymous No.8000903]

>>8000756
Don't listen to the dumbfag, double majors aren't even challenging unless you're doing some engineering major with a booked up schedule, math and bio are both pure subjects that leave a lot of extra room in your schedule and both would definitely work as a double major.

That is, committing to 2 whole majors before you start college is kinda silly, most people end up changing even their one major, but don't rule it out, it's doable. It's a lot of work unless you pick subjects that complement each other like math/physics but not too much.

[Anonymous No.8001322]

How do I git gud at math

I feel like a piece of shit for not being able to understand lessons very well and having to spend most of my study time on it

[Anonymous No.8001369]

I'm 18 but I look 14. I have a deep voice, a relatively high amount of body hair (no facial hair) and a pretty well developed body except for the fact that I am a manlet. Wtf is wrong with me? Am I a late bloomer or is my puberty broken?

[Anonymous No.8001400]

>>8001369
Become girl.

[Anonymous No.8001747]

>>8000767
Thanks anon, will do. Extra semester isn't too bad but a counselor would know my situation best.

>>8000903
Oh I'm for sure not commuting yet it's just an idea I've been having, wanted to do something science related for a long time but have a hard time deciding on one subject. I realize they don't compliment each other greatly as bio is a lot less math heavy than Chem or physics but I think it would be interesting to try to use them together in some way, if not at least I'm happy knowing both.

[Anonymous No.8001932]

>>8000888

Hence my earlier mention of Riemann's little paper on number theory. :^) nice double-trips btw

[Anonymous No.8001954]

I've heard someone say PCA differs from FA in the sense that it isn't a "statistical linear model" or something. How come is FA linear model but PCA not? What is linearity here?

And what the heck is an eigenvalue in the context of FA?

[Anonymous No.8002003]

Why the fuck is this a named reaction?

[Anonymous No.8002041]

energy is a concept used everywhere but its foundations still don't make sense to me

[Anonymous No.8002049]

i have a stupid question

[Anonymous No.8002059]

>>7999343
Bump, don't ignore me you faggots, if it's so ez then explain it to me!

[Anonymous No.8002062]

>>8001369
faggot
>>>/r9k/
>>>/b/

[Anonymous No.8002064]

>>8002059
if a=b then 1/a=1/b

[Anonymous No.8002099]

How much does job experience matter for getting a STEM job?

I was planning on interning next summer but my dad wants me to get a part time job this summer in a grocery store or something. Is he right?

[Anonymous No.8002110]

What's the like, fundamental truth regarding the difference between a population and a sample? It just seems sort of arbitrary to me

[Anonymous No.8002111]

>>8002049
Because it doesn't scale linearly
e = 1/2m*(v SQUARED)

[Anonymous No.8002305]

How do you take notes /sci/?
I'm studying from walter lewin's lectures + a book, but I think my method of taking notes is too shitty. I tend to forget half the lecture, is there a note taking guide or something like that? Excuse me for being a brainlet, just self-studying because I don't want to be too retarded. (Also, taking notes from books?? I don't really get it, can anyone point me towards a study method?)

[Anonymous No.8002312]

>>8002305
I'm struggling with the same fucking problem

[Anonymous No.8002333]

If I'm studying calculus, do I ready need to know or understand the proof of something? Isn't it enough just to know that a formula or equation always works a certain way?

[Anonymous No.8002344]

>>8002305
Really the repetition is what helps me. If a professor is explaining a problem, I not only write down the steps but include a summary of how that step was executed in the margin. If you're self teaching, you can also pause the lecture, go over the notes you have, and include any other observations you have in the margins before jumping back into the lecture. As far as books, just highlight the points and write those down in a separate notebook. I can give examples if you want.

[Anonymous No.8002353]

>>8002344
Please do.

[Anonymous No.8002374]

>>8002333
If you're not a math major OR you aren't a physics major OR you aren't an engineering major OR you aren't taking any higher level math (anything past Calculus I), then you will probably be okay not knowing a lot of the theory.

Otherwise, take the time to at least understand the idea / theory behind calculus at a basic level.

[Anonymous No.8002379]

Should I keep going with CS ?


I just finished my first year of college and I'm not sure if I want to do programming for the rest of my life.

[Anonymous No.8002380]

Can someone explain what blackbody radiation is from the big bang? So the light from the big bang is traveling towards us. Is this light from the edge of the universe? Will all the light from the big bang eventually reach us and there will not longer be any blackbody radiation?

[Anonymous No.8002385]

>>8002379
CS doesn't necessarily mean you will have to get a job as a software developer.

Maybe check out CE or EE?

[Anonymous No.8002390]

>>8002385
I wish I knew what other stuff was like. I don't really have any way to get an idea of it. I would have done mech e but I hate doing anything related to CAD. Had an engineering class in highschool and I sat in front of a laptop making things for an hour a day.

I should probably watch youtube videos or something.

What is being an EE like?

[Anonymous No.8002395]

Engineering major here, in my applied quantum mech class we're discussing density matrix formalism, can anyone recommend a good reading resource to learn more about this? Also looking for recommendations for anything related to WKB approximation

[Anonymous No.8002409]

>>8002390
No idea. Typically a good amount of overlap with computer engineering. A bare minimum of CS.

Here is the EE program at my university, it's probably very similar to EE programs across the country. Basically it's part physics (electricity and shit, obviously), part math, part CE (computer architecture, microprocessors, etc...), with a sprinkle of CS.

[Anonymous No.8002412]

>>8002409
https://www.ship.edu/Academics/Programs/Undergraduate/Electrical_Engineering/

Forgot the link.

[Anonymous No.8002414]

>>8002409
It would be easier if I could be interested in something. I don't know why but I've never been interested in anything so I just decided on CS randomly.

[Anonymous No.8002415]

If I have a standard normal distributed random variable X with mean μ and variance σ2, what is a confidence interval again? Specifically, what is the 95% confidence interval?

[Anonymous No.8002416]

>>8002409
At my uni there are big parts related to signal processing as well as RF and the like

Lots of matlab

[Anonymous No.8002422]

>>8002379
Depends, you could go into theoretical computer science if your university offers this track. It is basically applied mathematics however. Look up some classical computer science problems and see if those do anything for you. If your uni is worth its salt itll offer some actual computer -science- classes besides programming as well after your first year. Have you looked into that?

If you decide to stick with computer science it does not neccessarily mean youll be stuck programming. You could go into an advising role (consultant), or if you play your cards right something quantitative or a managing function.

[Anonymous No.8002424]

>>8002422
Eh, right now I'm going to a community college and getting a transfer degree, so they don't really offer any of that stuff.

I'm just worried about not knowing enough and not being able to get a job. Something where you get a degree or pass a test and get certified, and that proves you can do a job seems like it would be less scary.

[Anonymous No.8002428]

>>8002414
It's never a good idea to randomly pick a major. If you're STEM minded, but not very good with math, and have no interest in programming, then maybe check out biology? I don't have any good advice for you, considering I know nothing about you.

I get the feeling that maybe you'd be better off in a business major or something similar. I knew a guy who was really smart, majored in Physics, got beat down, and went into Finance. He's doing pretty well now.

[Anonymous No.8002433]

>>8002428
I don't even have any idea if I'm math minded or not.


I'm in precalc now and I have an A, although that doesn't really mean anything.
Never took anything hard in highschool because I didn't want to do more work.

[Anonymous No.8002435]

>>8002424
That's a normal feeling for a freshman. Maybe you should stick with it, keep improving yourself, keep practicing, have a positive mindset, and you'd be amazed what you can do. Sounds cheesy, but it's true. People underestimate themselves all the time.

[Anonymous No.8002438]

>>8002433
haha, if you got an A in precalc, then calc I is gonna be a joke.

anyways, I've given you enough to think about. Best of luck.

[Anonymous No.8002439]

>>8002424
>I'm just worried about not knowing enough and not being able to get a job.
The longer you study, the more you become aware of all the things you do not know.

You should make a list for yourself of some alternative majors, a cs major, and all their pros and cons.

[Anonymous No.8002462]

>>8002439
>The longer you study
I don't really study though. I just complete the homework and that's it.

[Anonymous No.8002468]

>>8002462
You could always do some extracurricular ideas. Just throwing down some ideas.

[Anonymous No.8002469]

>>8002380
We don't see as far back as the big bang only the epoch of recombination which is when the universe became transparent.

It's not quite the horizon, non-light based methods like neutrinos and gravitational waves could probe further but back then light couldn't travel far so none of it survives to this day. It is very near the edges of the observable universe.

At each moment CMB light reaches us so we see a slightly further away patch of the universe the next time we look which recombined at the same time but the light took longer to get here because it was further away. (in reality we don't see one exact part, recombination wasn't instantaneous). In non-accelerating cosmologies this could go on forever, seeing more and more distant light with the CMB moving to longer wavelengths. However with dark energy the horizon is limited so the CMB will in the very distant future disappear.

[Anonymous No.8002472]

>>8002468
That's why I'm unsure in what I'm doing. Other people seem to care about CS and do extra-curricular stuff and read about thing etc.

I just get the homework done and then look at 4chan/play videogames sometimes.

[Anonymous No.8002484]

>>8002469
I remember reading somewhere that the James Webb Space Telescope will help us probe even earlier into the universe. If this is true and you're aware of it, how is it possible if for JWST to see past recombination? What makes it different from Hubble?

[Anonymous No.8002487]

Are there any people here who are working with a mathematics degree?
What kind of work can I expect to be doing with one?

I'm two years into a math major and I'm starting to get the feeling I should start career planning before it's graduation and I need a job ASAP.

[Anonymous No.8002491]

>>8002472
this is why I changed out of CS. it seemed like you had to make your whole life CS. not working on coursework? go make some apps or build some websites or you'll NEVER get a job.

the companies in the industry have really shady practices too, they'll say that they need a ton of new engineers but at the same time are firing a lot of the older ones.

[Anonymous No.8002496]

>>8002491
What did you change to?


Also I think my problem is more of a general can't care problem.
I wonder if I have brain problems sometimes.
I probably have autism or something.

[Anonymous No.8002504]

>>8002496
I'm in electrical engineering now.

I have the same mental thing as you. I really do not give a shit about this stuff but I'm not bad at it so I don't really know what to do. I don't really care about anything.

[Anonymous No.8002597]

It's 1am and I can't think for shit. Can anyone help me?

[Anonymous No.8002603]

>>8002487
Finance basically
So banking, accounting, actuarial etc
Companies like giving internships to math majors, try to get one the summer before your senior year

[Anonymous No.8002613]

>>8002597
...........

[Anonymous No.8002617]

>>8002613
I know its just basic addition/division, but I'm a lazy fuck.

[Anonymous No.8002620]

>>7997244
Question: What are some good Algebraic methods of simplifying polynomials of degree 2 or higher in order to find their roots?

[Anonymous No.8002621]

>>8000672
arithmetical series ...i thought people learned that in high school ?

[Anonymous No.8002622]

>>8002469
great answer. Thank you

[Anonymous No.8002625]

>>8002059
if a=2 then 1/a=1/2 dumbfuck

[Anonymous No.8002641]

>>7999920
recognizing microexpressions has nothing to do with empathy , you can memorize them by definition (scrunched eyebrows and pursed lips is anger ) where a psychopath is a highly manipulative person and will learn that and read them correctly exactly because you lack empathy ...empathy is more of a feeling in recognising emotions and social situations where you share an emotional connection with someone (making someone feel bad makes you feel bad, making someone feel good makes you feel good) so sociopaths don't pick up on those feelings (can make them seem rude or uninviting if you unintentionally hurt someones feelings because you just don't understand or don't care that what you are saying is hurtful )
there is no correlation in empathy and being analytical but it can make some hard decision making targeted twoards others (firing someone or dealing a death sentence etc. )

[Anonymous No.8002654]

>>8002620
Check for easy roots : 0, +/-1, +/-2, +/-i
If the polynomial is biquadratic (ie of the form ax^4 + bx^2 + c), then make the change of variables u = x^2. You now only have to solve quadratic equations.
If the polynomial is palindromic (ie. the coefficients are symmetric with respect to the middle one) with even degree, then you can make the change of variables u = x+1/x. You have now reduced the degree by half and will only have to solve a bunch of quadratic equations in the end.
As a general rule of thumb, it is always easier to solve two equations of small degree rather than one equation of large degree.
If you are looking for rational roots with a monic integer polynomial: Study the function (ie. differentiate it, graph it and estimate the location of zeros). The zeros are then actually integers, therefore very easy to check if you have even crude bounds on the intervals where the function vanishes

[Anonymous No.8002731]

>>8002484
It's not true i'm afraid but it would be nice. What JWST will do is see earlier than the Hubble deep fields to some of the earliest galaxies.

At recombination there were no galaxies or even stars. After recombination the gas just cooled and started collapsing. Only radio has a chance of looking into the dark ages. Then there was first light with the first generation of stars, that is the earliest a optical infrared telescope (like JWST or Hubble) will see (barring exotic things like primordial black holes).

Hubble is limited to galaxies at about redshift 10, simply because it's instruments don't go very far into the infrared. As you go to higher redshifts as I'm sure you know the observed light is at longer wavelengths, this is fine until the source isn't emitting at the shorter wavelengths. This lyman break is where the hydrogen gas strongly absorbs the UV cutting off the blue tail. The lyman break is used to find the highest redshift galaxies but it also means you cannot find these objects if you can't work in the infrared. The further you go the deeper you can go. JWST will get to at least redshift 15 perhaps 20 with help from big surveys from other telescopes to find extreme objects. Recombination happened about redshift 1100!

You may be confusing the epoch of recombination with the epoch or reionisation, the latter of which is a hot topic and one of the key goals for JWST and the coming generation of 30 meter class telescopes. After first light the gas in the universe was heated and at some point recombination was reversed. We don't know exactly when or how it happened but it was around redshift 7-12. The problem is it's quite hard to study. Hubble isn't sensitive enough to show us the faint galaxies back then so we don't know many there were and we have to extrapolate. JWST will change that.

....

[Anonymous No.8002732]

How do I find the derivative of 2^x?
I can find plenty of stuff saying what to do, but it leaves me wondering how they arrived on that conclusion.

[nokosage No.8002746]

>>8002732
Alright. At first we take the change of the function and divide by dx:

(f(x+dx)-f(x))/dx=2[(x+dx)^2-x^2]/dx=2[x^2+dx^2+2x*dx-x^2]/dx=2[dx^2/dx+2xdx/dx]=2[dx+2x]

Then we let dx->0 and we get df/dx=2[2x]=4x

QED

[Anonymous No.8002747]

>>8002731
The big advance with JWST is not just sensitivity and wavelength but also information. Hubble gives us almost nothing on these high redshift galaxies. At best a crude redshift and some information about the age of the stars. JWST gives us not just imaging but spectroscopy, it has a very good spectrograph which will measure the brighter high redshift galaxies in detail. Hubble on the other hand despite having a magnificent UV spectrograph (which I am working with) can't really do sensitive infrared spectroscopy.

JWST won't be sensitive enough to see the first stars but there is a slim chance it could see the death of one. These would be the spectacular supernovae of hundred solar mass stars.

It's going to be quite transformative. It probably won't rewrite cosmology but it could rewrite galaxy formation. The pictures should also be superb.

[nokosage No.8002751]

>>8002732
Shit, I misread.
You know that the derivative of exp(k*x)=k*exp(k*x) right?

So we have:
2^x=exp(ln(2)*x)
so differentiating it we get: df/dx=ln(2)*exp(ln(2)*x)
remembering that exp(ln(2)*x)=2^x we substitute that in getting:
df/dx=ln(2)*2^x

[Anonymous No.8002755]

>>8002751
How badly did you fuck up to misread "2^x" then give an insanely complicated answer?

But anyway, what I don't get is how you got to exp(ln(2)*x). x=e*lnx makes sense at least.

[Anonymous No.8002775]

>>8002099
relevant experience > experience > attitude > how well you did in uni > what you did in uni, assuming identical qualifications
Do unpaid internships.

[Anonymous No.8002820]

What are applications like the Mean Value Theorem and Newtons Method actually used for?

[Anonymous No.8002823]

>>8002620

For all univariate (one-variable) polynomial equations, you can transform it into an equivalent /monic depressed univariate polynomial equation/, or what I refer to as an "MDUPE". A monic polynomial is simply (trivially) a polynomial whose leading coefficient is one, while a depressed polynomial is simply one whose next-highest term vanishses/has a coefficient of zero. depressed polynomials were used to solve cubics and quartics back in the day.

What I am describing is a special case of what is sometimes called a "Tschirnhaus transoformation", but it turns out to work for all polynomials, regargless of degree. In the case of low-degree polynomials, it can constitute the first few steps in a general algorithm to find those roots, and it may apply in special cases for higher degree polynomials. There's three steps: a trivial one, an interesting one, and a tedious one.

1) (trivial): divide through by the leading coefficient.

2) (interesting): make a substitution of variable of the form [math] \displaystyle x = t - \frac{b}{na} [/math] , where x is the variable of the original polynomial, t the substitute variable, a the original polynomial's leading coefficient, b its next-highest coefficient, and n its degree.

3) (tedious): rearrange in terms of your new variable t.

Works for all polynomials but I have to review details. pic related is part of an article I'm writing myself on the topic, ideas I've hashed out in previous /sci/ threads.

[Anonymous No.8002850]

one set theory problem has me hung up

let A be a set with n+1 elements, where n is in the set of whole numbers. Let s be in A. Show that A \ {s} has n elements.

(equinumerosity)

It's the last problem so I'm about to say fuck it

[Anonymous No.8002866]

>>8002820
The mean value theorem is used often in proving that someone was speeding. If you ever see "speed enforced by aircraft", the way they do this is record the time it takes your car to travel between two known points and from there compute your average speed. Per the mean value theorem, there was a point on that interval where your instantaneous speed was equal to your average speed and therefore you were speeding. There used to be devices actually in police vehicles that would do this - they measure the distance between two easily identifiable points, input this to some device and then press a button when you hit the first point and again when you hit the second and it does the calculation. This system has largely been dropped (at least in the US) in favor of radar systems that give actual instantaneous speed.

Newton's method is used in optimization to find the zeros of a function (specifically the derivative), but I'm not too familiar with optimization problems

[Anonymous No.8002867]

My teacher said that this problem could be solved by energy or by angular momentum.
Is he ling or am I shit?

[Anonymous No.8002870]

>>8002867
you're shit.

[Anonymous No.8002871]

>>8002867

[Anonymous No.8002874]

>>8002870
Fugg.
I suspected so.
Thanks anyway.

[Anonymous No.8002890]

>>8002870
>>8002874
I have no idea how I'd start with solving this through energy, then.

[nokosage No.8002913]

>>8002755
Ok, let's do this:
ln(2) is the natural logarithm of 2.
2=exp(ln(2)) right?
now, (e^k)^x=e^(k*x)
now 2^x=(e^ln(2))^x=e^(ln(2)*x)
now, for f=e^(k*x), df/dx=k*[e^(k*x)]
if we then infer that since 2^x=e^(ln(2)*x), we can substitute k for ln(2), we get that 2^x differentiated is ln(2)*(2^x)

[nokosage No.8002936]

>>8002867
Let's call the angular momentae when only one of them is spinning L and when they're both spinning equally fast J.
We call the angular frequency before w, and the one after v (limited by fonts here)

We then have by conservation of angular momentum: L1+L2=J1+J2
=½(M1)(R1)(w)
=½(v)[(M1)(R1)+(M2)(R2)]
so we just isolate v:
v=(M1)(R1)(w)/[(M1)(R1)+(M2)(R2)]

Index 1 indicates the values of the one that spins at first, and index 2 the other one.
Put in the numbers. Win.

[Anonymous No.8002951]

>>8002913
Isn't angular momentum L = Iw?
The paper states that I = (1/2)MR^2.
Why haven't you squared the radius?

[nokosage No.8002953]

>>8002951
I fucked up because I'm retarded.

[Anonymous No.8002955]

>>8002951
Sorry, guy deleted his post and I responded to you by accident./

[Anonymous No.8002958]

Sorry for what's probably a shitty way to type this:
If D^[n-1]x^n= (n(n-1)...2)x, then why does D^[n+1]x^n=0? Apparently D^[n+1]x^n is the derivative of a constant but D^[n-1]x^n is not, and I can't wrap my head around why that is.

[Anonymous No.8002961]

>>8002953
I suspect that my momentum method is correct, but my teacher told me that the problem can be solved by energy methods. I have no idea where I'd start with that.
He frequently makes petty mistakes and and is often sleep-deprived so I really don't know which of us is wrong. He could mean "you can solve it through energy methods which you don't have the tools for yet."

[nokosage No.8002975]

>>8002951
This is analogous to complete inelastic collisions where conservation of momentum states that m1vi=(m1+m2)vf, vf=vi*m1/(m1+m2)
while conservation of energy states:
½m1vi^2=½vf^2(m1+m2), so vf=vi*sqrt{m1/(m1+m2)}

Change speed to angular frequency and mass to moment of inertia.

Now, the answer to this is that energy is lost to heat and shit. You cannot get the same result from them.
Conservation of angular momentum dictates the end angular speed.
Good luck son.

[nokosage No.8002982]

>>8002958
D(x^n)=n*x^(n-1)
for a being a whole, positive integer smaller than n:
D^a(x^n)=n!/(n-a)!*x^(n-a)
for a=n-1 we get
D^(n-1)(x^n)=n!*x which is a line.
D^n(x^n)=n! which is constant.

[nokosage No.8002985]

>>8002961
See post >>8002975

[Anonymous No.8003000]

>>8002975
Completely forgot about elasticity stuff.
I usually do the homework and problem sets, and review the all the class in the week preceding the test. The next test is in a little while, and it's been a month since elasticity, which hasn't come up again. I should try reviewing small portions of such at more frequent intervals. Thanks (and thanks to >>8002870) for the heads up.

[Anonymous No.8003009]

>>7997244
If you know the four basic radians of the unit circle: pi/6, pi/4, pi/3, pi/2.... etc.

Is there a way to find their corresponding values in the other quadrants? Other than figuring out what the angle is and then converting it radians.

For example, if I have pi/6, and I want to find its corresponding value in the fourth quadrant, 11pi/6, how can I do that?

Preferably, something where I can add units of pi to the radian I already have.

[Anonymous No.8003016]

>>8002823
Damn son. I'll try this. Right now I'm in Differential Equations jutsu, and in order to solve for the general equation you have to factor it out properly.

Its a pain in the ass once the degree is four or higher.

[Anonymous No.8003021]

>>8003009
Just use your head man. Draw a sketch of the axis, label where you are and what quadrant you want to be in and then just use basic (and I mean BASIC) arithmetic. Practise it a bit and you'll be good at it within a week. Never underestimate the importance of sketches, especially when it comes to radians, vectors and complex numbers.

[Anonymous No.8003024]

I am trying to assist in teaching a "grocery math" class, and I am trying to establish a formula to solve a word problem I've been given. I have spreadsheets and shit that do it for me when I'm working, but I want to understand. Please help.

"If you sell $1000 of a 25% margin item, and your target margin is 50%, how much do you need to sell of a 75% margin item to end at target? How about 2 items at 60% margin?"

[Anonymous No.8003112]

so in the deep end of mathematics, i've noticed circles talking about algebra vs geometry
what exactly characterizes algebra and geometry?
i know there's some REALLY deep stuff involved, and i've just completed complex analysis, but i don't want a hand-holdey answer

[Anonymous No.8003215]

>>8003024
[math]\frac{250+.75*x}{1000+x) = .5[/math]

[Anonymous No.8003223]

>>8003215
Well it worked in the preview, I must've made a typo

[math]\frac{250+.75x}{1000+x} = .5[/math]

[Anonymous No.8003254]

>>8003223
How about 2 items at 60%?

[Anonymous No.8003258]

>>8003254
I don't quite understand what you mean by that, sorry

[Anonymous No.8003260]

>want to look up linear constant coefficient difference equations
>Google considers difference to be the same as differential

[Anonymous No.8003280]

Is IQ meaningful? And could someone link studies supporting their answer?

[Anonymous No.8003284]

>>8003258
It's cool, I was able to figure it out.

{Sales(AMargin%) + x(Bmargin%)]/(sales + x)=Zmargin %

[Anonymous No.8003290]

>>8003280
No. I tested at the 97th percentile, and I'm dumb as a box of chocolates. Actually, just yesterday, I hurt myself getting out of bed. Went to grab the covers to throw them off of me, jammed my thumb directly into my nipple. Hurt for like half an hour. Not even kidding.

[Anonymous No.8003292]

>>8003290
No offense, but anecdotes don't constitute science.

[Anonymous No.8003297]

>>8003260
try quotation marks

[Anonymous No.8003301]

>>8003292
See?

[Anonymous No.8003319]

C++ help

basically my c++ homework is asking to construct a simple atm where the code with calculate the new balance after a withdraw or deposit has been made. Can someone assist me with creating a function for my cases?

[Anonymous No.8003324]

>>8003297
Dzięki

[Anonymous No.8003341]

>>8003319
cout<<"enter withdraw:";
cin>>with;
if(with>balance)
cerr<<"you fucked up nigger\a\a\a\n";
else
balance-=with;

[Anonymous No.8003367]

>>8003341
thank you for the code and another stupid follow up question, do i insert all of this within case 2?

[Anonymous No.8003372]

Why is the electric field from an infinite plane constant?

[Anonymous No.8003378]

>>8003319
I'll write it for you

Int main(){
run = true;
int balance = 0; //don't what intital is
while(run) {

string action = "none";
int amt = 0;
cin >> action;
If(action == "quit") {run = false; break;}
else if (action == "deposit")
cin >> amt;
balance += amt;
else if (action == "withdrawl")
cin >> amt;
balance -= amt;
else
cout << "Invalid Action! Valid actions are 'deposit', 'withdrawal', and 'quit' \n"

}

}

[Anonymous No.8003395]

>An electric motor turns a flywheel through a drive belt that joins a pulley on the motor and a pulley that is rigidly attached to the flywheel as shown in the figure below. The flywheel is a solid disk with a mass of 55.5 kg and a radius R = 0.625 m. It turns on a frictionless axle. Its pulley has much smaller mass and a radius of 0.230 m. The tension Tu in the upper (taut) segment of the belt is 175 N, and the flywheel has a clockwise angular acceleration of 1.67 rad/s2. Find the tension in the lower (slack) segment of the belt.

I got the answer by assuming the flywheel has a moment of inertia of (1/2)MR^2 but some things online say I should be able to find the angular momentum of the pulley and start from there.
The hell do I do that?

[Anonymous No.8003401]

How would you find the value of something like [math]\sum _{n=1}^{\infty } \frac{1}{(4 n+1) 3^{2 n}}[/math]?
I think I probably have to substitute [math]x=\frac{1}{\sqrt{3}}[/math] to get [math]\frac{\sum _{n=1}^{\infty } \frac{x^{4 n+1}}{4 n+1}}{x}[/math] and then derive it, but how can I just say [math]\frac{1}{1-x^4}=\sum _{n=0}^{\infty } x^{4 n}[/math], and integrate to get [math]c+\frac{4 x^3}{\left(1-x^4\right)^2}=\sum _{n=0}^{\infty } \frac{x^{4 n+1}}{4 n+1}[/math] then divide by x? I don't think I can just get rid of the c, can I? I mean, if I substitute 0 I get that c=0, but does that let me just leave it off?

[Anonymous No.8003409]

Ok so if we have a group of 10 elements, prove that the number of elements x in G such that x^5 = 1 is divisible by 5.

I had this on a test and I don't think my answer was right.

[Anonymous No.8003417]

>>8003409
What does the first half of your first line have to do with the second half?

[Anonymous No.8003433]

>>8003378
>>8003341
thank you both anon, im going to call it a night and continue this tomorrow evening

take care

[Anonymous No.8003474]

In the current year, would it be possible to use miniature atomic explosions as a propulsion method for high-speed, long-distance travel?

The spacecraft can still leave the atmosphere using conventional propulsion methods (rocket+detachment stage), so radiations can't cause damage, then last stage would use the miniature explosions only.

As alternative the spacecraft could also be launched from a station already outside of the atmosphere.

Thoughts?

[Anonymous No.8003498]

>>8003409
have you already learned the sylow theorems?

by sylow's 1st theorem there exists an element of your group of order 5, take a generator y.

then 1, y, y^2, ..., y^4 are all in the subgroup of things satisfying x^5=1

by lagrange's theorem the subgroup of things which satisfy x^5=1 divides 10, and its at least 5 so it's either 5 or 10 which are both divisible by 5

[Anonymous No.8003501]

>>8003409
That's not true
In the additive group Z_10, 0 is the only element that satisfies x*5=0

[Anonymous No.8003506]

>>8003401
Use [math]\frac{x^{n+1}}{n+1} = \int_0^x t^n dt [/math].
You get
[eqn]
\sum_{n=1}^\infty \frac{1}{(4n+1) 3^{2n}}
= \sqrt{3} \int_0^{ \frac{1}{\sqrt{3}} } \sum_{n=1}^\infty t^{4n} dt
= \sqrt{3} \int_0^{ \frac{1}{\sqrt{3}} } \frac{t^4}{1-t^4} dt
[/eqn]
Which is straightforward to evaluate.

[Anonymous No.8003610]

Yo can someone verify that I'm doing correctly? I haven't been to class because I've been busy and we have a test on this stuff tomorrow.

If someone can look at what I did and tell me if it's right or wrong that would be great. Just need help with this problem.

pic related

[Anonymous No.8003628]

>>8003610
Can you post a good pic, can't read that

[Anonymous No.8003629]

>>8003610
looks good but usually the fundamental set is the set of all {c_1 e^{-x}+c_2e^x+c_3e^{-2x}} where c_1,c_2,c_3 are any numbers, not the thing you wrote below it unless that's some notation you use in class

have you tried actually plugging that y into the differential equation and seeing if it works?

[Anonymous No.8003633]

If I were listening to music inside a soundproofed vehicle, then accelerated last the speed of sound... What would it sound like?
Would there be some crazy doppler effect or silence or what?

[Anonymous No.8003642]

>>8003633
The vibrations would accelerate relative to you and cause ear damage due to a lack of dampening due to soundproofing.

[Anonymous No.8003651]

>>8003628
I just recreated it in onenote, the camera on the surface is shit. pic related


>>8003629
Yh, that's the notation our professor uses it. Just the first time I see the Dy in the equation, wasn't sure if I had to the it the same way I had the other problems or use a different method.

I actually haven't, how do I do that?

[Anonymous No.8003701]

>>8003651
I just mean that your y=... is supposed to be a solution for the differential equation you started with. And so you can plug it into D^3y-2D^2y-Dy+2y and hopefully get 0.

[Anonymous No.8003721]

>>8003642
Oh... Makes sense.
If it wasn't soundproofed?
Less ear damage but still a cacophony?

[Anonymous No.8003789]

>>8003506
Straight forward? Doesn't that involve tanh? Or is wolframalpha being a bully?

[Anonymous No.8003791]

Having trouble with this truth table, particularly the first step - ~D● (B v A) →~C how do i work this out? Do i need to split this in to two parts?

Thanks in advance /scii.


~D● (B v A) →~C
~B v C
D→ (C●B)
--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐--‐
C → D

[Anonymous No.8003795]

I already asked /adv/, no luck.

If anyone knows about graduate admissions, and can help me out I'd really appreciate it.

I did relatively well my first two years of college. I had a ~3.5 GPA, was involved in research, and a couple small-time programs. In the second semester of my junior year I was diagnosed with Cushing's disease. It's a brain tumor of the pituitary gland. I've had surgery two different times to remove it (March 2014, and August 2015). I'm going to be graduating this May with a degree in Mathematics, and approximately a ~3.1 GPA.

Until my tumor happened I had always thought I'd go on to get my PhD in mathematics, but I feel like the actual me wouldn't show through on an application.

My question is this: is there any way to communicate this situation on an application to graduate school? My professor from research my first two years will 100% vouch for me, but I transferred closer to home after I was diagnosed, and honestly only have 1 or 2 people that would write a recommendation for me here.

Thanks for any help.

[Anonymous No.8003878]

>>8003789
Never mind, I realized you can get it apart into nicer fractions.

[Anonymous No.8003886]

>>8003721
Nah just fucking with you anon i made that up completely

[Anonymous No.8004488]

Could anyone explain this to me, x=time needed to fill up a pool through first pipe and y=time for the second. If pipe x needs 8 hours longer to fill up the pool than the pipe y, why the fuck is it written as x=8+y then?? I just can't wrap my head around this, even though it's trivial as fuck. If y does the job of x in 8 hours less, or x does the same job as y, only that it takes 8 hours longer, why isn't it then y=x+8? Please please please, just tell me what I'm missing here...

[Anonymous No.8004540]

>>8004488
What? If y is the amount of time it takes pipe 2 to fill up a tank, and we know that pipe 1 takes 8 hours longer than pipe 2 to fill up the pool, the time it takes x would be y (time from pipe 2) + 8 (the extra time that pipe 1 takes). Not really sure how that could confuse you.

[Anonymous No.8004545]

So I decided to shun away from physics first because I figured that aerospace engineering is more in line with what I wanna do. (Build Rockets)

Then I jumped ship to mech E this year because my understanding is that they are similar degrees and I can do more with mechanical.

Now, I haven't done a whole lot with mechanical engineering other than statics, but I'm currently enrolled in a physics III course for engineers. (Basically, tackling a lot of quantum physics, but doesn't get into relativity.)

So here's the thing - I am remembering why I wanted to do physics so much in the first place. it's absolutely fucking fascinating to me. I thought this course would be my most difficult, but I just fucking love it so much that the work really doesn't bother me. I also hear about all these cool physics projects and awesome mathematical concepts people in the physics department talk about, while engineering always seems kinda dull.

So I was curious /sci/, say I really wanted to go into physics/astrophysics, but I still want to be employed on some level. Is physics really a bad choice? Would dual majoring allow me some larger benefits? Perhaps another major entirely?

Any advice on this? I kinda just sperged out a bit, but I'm wondering if anybody ever faced similar decisions.

[Anonymous No.8004699]

>>8004488

Pipe x needs 8 hours MORE than y. So x = y+8. If pipe y needs 3 hours then pipe x needs 11; 8 MORE than 3.

[Anonymous No.8004702]

solve this pls?

[Anonymous No.8004706]

>>8004702
or just show me which integral I need to compute?

[Anonymous No.8004879]

>>8004699
>>8004488
Ok, I was thinking backwards. Basically, if X is a bigger value, and we equal that to the smaller value, in order for the bigger value X to be equal to the smaller value Y, we either have to fill the smaller value Y to match the bigger value X, or we can take away from the bigger value X, to match the smaller value Y. Thanks for helping clear the path to the enlightenment.

>don't mind me, just my OCD rigged brain forcing me to write all the "proofs" out so I can remember it easily, once again, appreciate it, thanks

[Anonymous No.8004885]

>>8004879
>>8004699
>>8004488
>>8004540
Sorry, I forgot to quote you, I was concentrating too hard on not fucking up Xs and Ys.

>this turned out to look way more autistic than I could've ever wished for, just end my life

[Anonymous No.8004891]

Is the electrical field inside a spherical cavity located inside a sphere of volume charge density [math] \rho [/math] zero, even if the cavity isn't concentric? Drawing a gaussian surface inside the cavity and calculating the flux through it, we should get [math] \vec{E} = 0 [/math], right?

[Anonymous No.8004896]

>>8004891
I worded this poorly, I meant that the field is zero, not that [math] \rho [/math] is zero.

[Anonymous No.8004901]

>>8004706
With a quick drawing, I'd say the figure you're looking for is (x^2 + y^2 - 1) + z^2 < 1, so that's the thing you have to integrate.

[Anonymous No.8004913]

>>8004891
If you have a sphere of conductive material and there you have a cavity without charge, then the electrical field inside the cavity is zero.
Proof:
Calculate the line integral of E on a closed path that pass though the cavity (pic related). Inside the conductive material, E is always zero, so if E isn't zero inside the cavity, the line integral on this closed path would not be zero and the curl of E would be non zero, thus E = 0.

[Anonymous No.8004914]

>>8004913
What if the sphere isn't a conductor?

[Anonymous No.8004917]

Where can i find information on what fluoresces at 365nm uv. I realize there is no reason to order information like that but I'm just wondering what sort of cool shit you could do with a 365nm uv led.

So far i know you can set dental cement and detect counterfeit money.

[Anonymous No.8004934]

>>8004914
idk, I guess that E != 0 in this case.

[Anonymous No.8004947]

>>8004917
Look up UV photography, it might give you some ideas

I recommend trying it out on plants in your garden, especially flowers

Don't forget your uv-proof goggles though, unless you want cataracts!

[Anonymous No.8004954]

>>8004934
Shouldn't the contribution to the cavity be zero? Since the line goes in and then out of it?

[Anonymous No.8004958]

>>7998862
So cool! This is what we are talking about in my heat transfer clas right now!

[Anonymous No.8005114]

>>8004958
wow so cool! what are u 12? kill yourself u faggot

[Anonymous No.8005118]

>>8005114
i love you :D

[Anonymous No.8005231]

Am I taking crazy pills or is this wrong? I feel fucking retarded right now, this should be easy as shit.

[Anonymous No.8005235]

>>8005231
Probably would have helped if I got the full fucking problem in frame, holy shit I need to sleep.

I'm not getting what they have on the third line though, which you can see all of. I have another (2-x)^2 below the Q_2*x^2

[Anonymous No.8005249]

>>8005231
>>8005235
Nevermind I'm a retard someone please kill me in my sleep.

[Anonymous No.8005362]

>>8003372
think about it like this. consider a point at the center of a finite disk. the field at the center is the sum of each charge around it, this makes the field there perpendicular to the plane of the disk, due to the symmetry (why would it point in any given direction along the face of the disk if every direction looks the same?). Only the perpendicular part of the field is left uncanceled out by a carge on the opposite end of the disk. Now as you add rings of charge to the rim of the disk, the radial vectors of the charges will be at shallower and shallower angles and they will be longer, these two facts reduce the perpendicular component of their contribution as well as the magnitude of their individual field, as a result you can get a finite magnitude from an infinite sheet. now you have an infinite sheet with a perpendicular field at its center, but the disk is infinite so everywhere is the center. This means that every where the field is exactly perpendicular to the plane. Now apply gausses law over a cylinder that has its circular bases on opposite ends of the sheet and you will see that now matter how long you make these cylinders there will always be the same flux through their circular bases of a fixed area and you will see that the electric field will not change.

[Anonymous No.8005659]

Info:
I've got to sell 3 kg of Apples, 2kg of Oranges and want to buy 1 kg of Grapes.
Independent and Normally distrubuted.

The expected values are A:30£, B:20£ and C:100£ per kg. The standard deviation is 20£ for all.

As the expected value for gains is pretty easy to figure out (30£), how would I calculate the probability of not making money/losing out on it?

[Anonymous No.8005748]

Hey guys. I asked my math teacher about finding (x, y, z) coords given longitude, latitude, and radius.

In response she gave me her old college textbook on Euclidean and non-Euclidean geometry, and only the very end brushes over elliptic geometry, while the majority is on hyperbolic geometry.

I'm 75 pages in (out of ~400), and it's pretty interesting, but I'm curious what the application is specifically for hyperbolic geometry, or if it's mainly pure math (not that there's anything wrong with pure math)?

[Anonymous No.8005815]

>>8005659
When you add up independent distributions, the variance simply adds up. This can be interpreted according to the pythagorean theorem.

[Anonymous No.8006145]

Is the chest pain during alcohol or benzodiazepine withdrawal due to ischemia? What about panic attacks?

[Anonymous No.8006497]

How do I get better at solving problems that I don't know explicitly how to solve?

For example, the kind of math problems where you have the tools to solve it but haven't learned exactly how.

[Anonymous No.8006550]

I'm trying to read about XRD but I can't figure out wth hkl and 001 002 100 200 etc are. Anybody?

[Anonymous No.8006638]

>>8006550
Also, why do we need high spectral purity? Why does it matter really?

[Anonymous No.8006675]

What is the fundamental difference between an axiom and a definition?

[Anonymous No.8006686]

>>8006675
in a definition you usually say
"We say that X is a P if X satisfies A, B, C"
in an axiom you go
"P is true"

[Anonymous No.8006695]

>>8006675
Definitions are just shorthand for common objects/attributes we don't want to write 500 times in a textbook. There's no truth or falsehood to them, they're just notation.

Axioms are propositions that we need to be true in order to do math properly, but can't prove.

[Anonymous No.8006722]

>>8006695
>truth or falsehood to them

Well if I go by
>>8006686
>"We say that X is a P if X satisfies A, B, C"

Aren't I asserting that the statement X is a P if X satisfies A, B, C" is true? By
>>8006695
>propositions that we need to be true in order to do math properly, but can't prove

Doesn't that make it an axiom?

Plshelp I'm trying to get into math but it seems so fucking wobbly. It is far more likely that I misunderstand than math actually being this wobbly.

[Anonymous No.8006726]

I'm a student athlete who trains 4-5 hours a day
I'm always tired all the time and find it hard to focus in class
My diet and sleep and everything is fine but my GPA isn't
How 2 b gud

[Anonymous No.8006758]

>>8005748
Relativity uses hyperbolic geometry

[Anonymous No.8006760]

>>8004958
Indeed, heat exchangers are pretty cool. I'm a ME, and I've been trying to remember how to do it.

Before you scold me for forgetting it, I've been working doing mechanical design for 5 years now so I'm a bit rusty on my heat transference knowledge.

[Anonymous No.8006764]

>>8003372
symmetry arguments

[Anonymous No.8006769]

i enjoyed algebra 1 and 2, but i disliked geometry. would i prefer pre calculus or statistics? i have to take one of them, and possible both depending on what UC i want to go to.

[Anonymous No.8006772]

>>8006726
train less or try taking a multivitamin.

[Anonymous No.8006779]

>>8006772
>train less
but muh olympic dream
i'll start taking multivits for the hell of it, any other tips for staying alert in class?

[Anonymous No.8006808]

Alright. So as we've all been taught, the difference between mass (kg), and weight (lbs), is that mass is a measure of how much matter something has, where weight is force resulting on a surface by the object, in respect to gravity.

Thus, an object that is not subject to gravity has no weight, where it still has the same mass if it were subject to gravity.

However, if we measure mass via a scale, and we also measure weight by a scale, how the fuck can we determine the difference? If we measure the mass of an object on earth, and the mass of the same object using the same scale on the moon, we're going to get difference masses.

So is the only way to determine the mass of something without a scale and subject to no gravity to already know the volume and density of the object? I'm assuming that is has to do with the relation that density = mass/volume is an applicable law where density = weight/volume isn't? But again, the measurement by scale method will still vary under different gravitational circumstances?

[Anonymous No.8006854]

>>8006808
>However, if we measure mass via a scale, and we also measure weight by a scale, how the fuck can we determine the difference? If we measure the mass of an object on earth, and the mass of the same object using the same scale on the moon, we're going to get difference masses.
Right. That is to say, a scale measures weight, from which we infer mass because we know the gravitational acceleration; and if our knowledge about that constant is wrong, then so is the measured mass.

>how the fuck can we determine the difference?
The question you should be asking here is: what does mass affect other than weight?

And the answer to that is "inertia". If I'm on the moon (or in deep space with zero gravity), and I'm looking at a high-mass object and a low-mass object, then it takes more force to move the high-mass object than the low-mass object.

If I'm floating in zero-gravity, and I'm holding a wrench (mass: a couple of hundred grams), then I can move it using my arm muscles just the same way I would on earth. But if I'm floating in space in between two massive objects -- say, my space shuttle and a landing craft -- then I can't grab both of them and move them relative to each other. Well, I can, but only very slowly, because my arms can only exert so much force and these two objects have a lot of mass, and therefore a lot of inertia.

So how do you measure mass? Clearly the easiest way is to measure weight and infer mass, which is why scales are very common and cheap. I'm sure it's possible to measure mass directly based on inertia or something, but that's not so easy and has all sorts of complications, so it isn't commonly done.

[Anonymous No.8006960]

Can you get AIDS from giving yourself a blow job?

[Anonymous No.8006966]

>>8006960
Only in Africa

[Anonymous No.8006997]

In a sample where the average IQ was found to be 115, is the occurence of someone with an IQ of 130 as likely as the occurence of someone with 115 would be in a sample with an average of 100?

[Anonymous No.8007017]

Need help. Check this out:

Int[0, π]
Int[0, 2π]
Int[0, 4]
ρ^5 sin(φ) cos(φ) dρ dφ dθ

---> (1/6)ρ^6 sin(φ) cos(φ) eval[0, 4]

= (4096/6) sin(φ) cos(φ)

---> (4096/12) sin^2(φ) eval[0, 2π]

= 0
(here's the problem)

---> C(ρ, φ) eval[0, 2π]

= C(ρ, φ)

Now if I make the bounds for φ to be [0, π] and those for θ to be [0, 2π], then I get:

(4096/12) sin^2(φ) eval[0, π]

= 4096/12

---> (4096/12)θ eval[0, 2π]

= (4096/6)π
(which I presume is the right answer)

Which is correct and why aren't those bounds interchangeable?

[Anonymous No.8007018]

>>8006779
Drink more water, or take a caffiene pill+ 2 glasses of water. Do everything on a very regular schedule, including your weekend. Sleeping, eating, studying same time every day. Kinda sux but if you insist on pushing yourself, so it must be.

Don't fall for the adderall meme, it's bad news.

>>8006722
No response for this?

[Anonymous No.8007119]

>>8006722
>Aren't I asserting that the statement X is a P if X satisfies A, B, C" is true?
What is P in this statement? P doesn't mean anything prior to the definition, so how do you evaluate this as true or false?

That's where the difference between definition and axiom is. Axioms are statements made completely out of prior objects (some basic objects we obviously can't define; these are called primitives) that we say are obviously true.

[Anonymous No.8007191]

First time in this board.
>Be me dropped obligatory school
>Some years later I find that I actually like science and math in general
Where the fuck do I start by myself?
Any legit online courses? (from very basics)

[Anonymous No.8007255]

>>8007191
probably some khan acadamy or coursera

[Anonymous No.8007288]

>>7998013
If your program is compiled to binary that means it's basically just processor instruction after processor instruction in form of binary numbers.
Each number stands for a specific operation (from math ops like addition or division to basic stuff like loading data in to a register or jump operations)
Each processor cycle the processor fetches the next operation and executes it.
What executing means depends on the operation of course. Your processor has an ALU (arithmetic logic unit) for basic math and a floating point unit for floating point math. So for math operations the operands are sent to the alu together with a signal that indecates the operation to be done. The ALU his circuits for addition, multiplication, etc. look them up yourself.
Jump instructions are pretty easy, your processor has an instruction pointer that points to the location in memory where the next operation to be executed is, so we just set that do the jump target.
The instruction pointer is typically a 32 or 64 bit register, aka a flip flop (if you don't know flip flops, you should probably look them up if you want to understand CPUs)

[Anonymous No.8007331]

Why don't we just eradicate all the mosquitoes on Earth?

They just spread disease and don't really serve any important role to anything...

[Anonymous No.8007340]

>>8007331
It's been talked about, but intentionally extincting a whole species isn't really something people want to do lightly. You never know what the implications could be from such a thing.

[Anonymous No.8007365]

My friend cultured this bad boy, what the fuck is it

[Anonymous No.8007477]

I know that the total number of divisors of a number is the product of one more than each exponent in its prime factorization. But how does one find the sum of all the divisors?

[Anonymous No.8007482]

What is the best book for getting back into Maths and Science for a guy with only a high school education in both?

[Anonymous No.8007537]

Is time travel consistent with ΛCDM, specifically as an explanation for non-zero Λ?

[Anonymous No.8007546]

>>8007477
not easily

for example perfect numbers (numbers equal to the sum of their proper divisors) aren't even known to be finite or infinite, and there's no knowledge on whether there are odd ones

[Anonymous No.8007591]

Would centrifugal force work in space to create artificial gravity like in sci fi films?

[Anonymous No.8007597]

Is it true that drinking carbonated water rots your teeth?

Like just normal tap water that I carbonated myself. My dentist swears up and down that this is awful and will give me cavities one day but I really like to do it and think it tastes refreshing and nice.

[Anonymous No.8007610]

>>8007591
I'm only a student so I may be wrong, but from a theoretical point of view, the first part of your statement would be correct. I don't know how they do it in sci fi films, though.

I recommend you to read the Chapter 9 of J R Taylor's Classical Mechanics for more info.

[Anonymous No.8007615]

>>7999930
((2i)(3i))^2 = (6i^2)^2 = (-6)^2 = 36. Nigga you dumb

[Anonymous No.8007634]

Any good book recommendations?
I am interested in Power Electronics, or Electrical Power Transmission and all that jazz.

I heard of the Bible: 'Art of Electronics" is good but I believe that it's more too focused on microelectronics rather than the ones I am interested on; is it?

[Anonymous No.8007677]

is it possiblwe to rape yourself?

[Anonymous No.8007681]

>>8007610
biologist here so this is a bit outside of my field, but yes i think so but only if you are on the inside of the spining object, or else the force lines will be pointing away and fling you off of the object rather than into the middle

[Anonymous No.8007715]

I need a book for tricks on how to parametrize curves.
Suggestions?

[Anonymous No.8008020]

>>8007546
>for example perfect numbers (numbers equal to the sum of their proper divisors) aren't even known to be finite or infinite, and there's no knowledge on whether there are odd ones

I meant, for example.
Find:
-Total Divisors of 600 (this one is easy)
-Sum of all divisors of 600 (I honestly have no idea)

[Anonymous No.8008111]

How do you come up with research ideas?

I'd really like to do some fungal research but I'm not sure what. I know fungi have wide applications that we haven't thought of yet but I don't know what they are.

[Anonymous No.8008146]

>>8007677

Yes, many people go to school for pure math all the time.

[Anonymous No.8008723]

>>7999652
If abs((ra-rb)/m)<1 it would be limited that way.

[Anonymous No.8008887]

Hi , I'm going to finish high-school soon and I signed up for a chemistry degree , on the wiki the books in the "High School - General Chemistry" category seems to be way bigger and deeper than my highschool's book , do they expand the different subjects seen during highschool or are they only for people who want to start from scratch ?

[Anonymous No.8008897]

>>7999910
>When you took the square root in step 4, you introduced the possibility of two solutions to the intermediate equation 36 = x^2.
Well yes. Two solutions for the new equation.

To be more precise he added a "apparent solution" (Scheinlösung) to the existing solution of the orignal equation.
To weed out the "apparent solution" it is necessary to check with the original equation.

We have to drop into the complex plane to check this. But we still get a real number solution? Is this a real valid solution in R? Probably not.

After simplifying through the complex plane we get.
[math]x = (-1) \times \sqrt[2]{36}[/math]

We take the root [math]\forall a \in \mathbb{R} : \sqrt[2]{a^2} = \left\vert a \right\vert[/math]
[math]x = (-1) \times 6[/math]
[math]x = -6[/math]

Or we square: [math]\forall a \in \mathbb{R} \land a \geq 0 : (\sqrt[2]{a})^2 = a [/math]
[math]x^2 = (-1)^2 \times (\sqrt[2]{36})^2[/math]
[math]x^2 = 1 \times (\sqrt[2]{36})^2[/math]
[math]x^2 = (\sqrt[2]{36})^2[/math]
[math]x^2 = 36[/math]
[math]\sqrt[2]{x^2} = \sqrt[2]{36}[/math]
[math]\sqrt[2]{x^2} = 6[/math]
[math]\left\vert x \right\vert = 6[/math]
[math]x = \pm 6[/math]

Therefore our proposed solutions to this equation are (apparent solutions were created through breaking equivalency by squaring):
[math]x_1 = +6[/math]
[math]x_2 = -6[/math]

Check our (equivalently transformed equation in the complex numbers; square roots of negative numbers are undefined in [math]\mathbb{R}[/math]) against our solutions.
Equation: [math]x = (-1) \times \sqrt[2]{36}[/math]
Calculate it: [math]x = -6[/math]

Test [math]x_1 = +6 \neq -6[/math] (Apparent solution detected).
Test [math]x_2 = -6 = -6[/math]

This is a bad example because we were able to easily calculate the right side.

[Anonymous No.8008910]

>>8008897
Different Example with no apparent Solutions because the starting Equation is already squared:
Original Equation(!): [math]x^2 = 4[/math]

Rewrite it just for clarification:
[math]x^2 = 2^2[/math] | Square-Root
[math]\sqrt[2]{x^2} = \sqrt[2]{2^2}[/math]
[math]\left\vert x \right\vert = \left\vert 2 \right\vert[/math] | Abs(2)=2
[math]\left\vert x \right\vert = 2[/math]
[math]x = \pm 2[/math]

Therefore we get:
[math]x_1 = \pm +2[/math]
[math]x_2 = \pm -2[/math]

Original Equation(!): [math]x^2 = 4[/math]
Test 1:
[math](x_1)^2 = 4[/math]
[math](+2)^2 = 4[/math]
[math]4 = 4[/math] (Valid solution)

Test 2:
[math](x_2)^2 = 4[/math]
[math](-2)^2 = 4[/math]
[math]4 = 4[/math] (Valid solution)

[Anonymous No.8009648]

How does maths become intuitive to me? How do I work on that? I've been studying maths seriously for couple of months so far. Before I just let it slide because I didn't want to bother back in high school. Now I'm taking a gap year and I'm currently on 2nd grade hs lvl maths and I love it.

[Anonymous No.8010669]

I don't know anything about Carl Sagan. Recommend some something to watch to introduce myself to him.

[Anonymous No.8010907]

>>8006997
The former situation is more likely as 130 is ~13% higher than 115 and 115 is 15% higher than 100.