/sci/ - Science & Math

>>10171975
how dangerous is nitrogen? Like if I accidentally flood a room with it and pass out and someone is nearby, do I stand a good chance of being revived?

once again degenerate anime nonce posters lower the credibility of /sqt/.
>thread before 310
>no "stupid questions thread" in title
>not using the pasta for the OP
kys, loser freak. for reference (i.e. do it fucking right next time) include the following the in title: /sqt/ - stupid questions thread / QTDDTOT, and this as the OP text:

For book recommendations, check the sticky and/or the /sci/ wiki. To download free books, check http://gen.lib.rus.ec/
For learning how to use the inboard latex, check the sticky. You can also test your latex before you post by clicking the "TEX" button in your reply box.
If your latex isn't working, it's because your adblocker is blocking it.
If you ask any question, remember that there is almost no universal notation:
>what constitutes a BAD question
If p divides |G|, show that there exists an element of order p.
or
GRUG DUMB DO GRUG'S HOMEWORK
>what constitutes a GOOD question
Suppose p is a prime that divides the order of a finite group G. Show that there exists an element of order p.
or
Grug think hard about problem. Grug show this much but grug can't make connection. What grug do?
previous thread: [insert when appropriate]

It's not hard to do and vastly improves the quality of the thread, since people generally just beg for fucking solutions if they're not told prior not to.

>>10172066
Nitrogen itself isn't dangerous. You're passing out from a lack of oxygen.

>>10171975
Fuck you for ruining sqt

>>10171975
Lurk more and then kys anyway

help please!
>>10171409

>>10172159
Isn't it flammable
t. Brainlet who doesn't know anything chemistry

>>10172221
Nope. 78% of our atmosphere is nitrogen.
I mean, you can get it to react with stuff, look up how fertilizer is made for instance.
You're probably thinking of a different gas.

Can somebody please explain what the distinction between a reversible process and an internally reversible process is? Why is heat transfer irreversible?

>>10172347
entropy

>>10172351
Explain pls

How do I study things like step by step guides on how to build things? Anki doesn't really help.

>>10172382

start by studying everything
then summarize the important parts
then trim the summary back until it's just a summary of the summary, continue until you just have a list of keywords
memorize the key words with a mnemonic device

>>10172389
This is difficult for me because it basically boils down to a bunch of measurements and exceptions to rules. Mnemonics don't work for me because I'm not an 18 year old girl who uses highlighters and liquid paper to study.

>>10172209

Your question is terrible and doesn't deserve to be answered. Try rephrasing it.

>>10172395

Yeah no shit it's difficult.

Can someone help me understand how to do this probability problem for my math stats course?

Let's say that I have a datafile including every baseball team in the MLB including their team stats. The question asking me what process I would take to compute the probability that the red sox would be included in a sample size of 2. The probability of selecting each team is proportional to the total number of home runs scored

>>10172355

Because entropy would decrease if heat transfer was reverseable. That's why it's a "Law of Thermodynamic" because it doesn't have to explain shit, it just works like that.

>>10172420
>the probability of selecting each team is proportional to the number of home runs
Imagine I have a list of home runs, and I pick one randomly. It's either by the red sox or not, and calculating the chance of either is trivial. If it isn't, I remove all home runs that team has made, and pick a new random homerun.
Sum the possibilities.

>>10172066
If you have hypoxia for long enough your brain will swell. The nitrogen won't cause any damage, but your swollen oxygen starved brain will turn you into a veggie

Is string theory a dead end or can it be updated to work with quantum mechanics?

>>10172145
absolutely fucking based

a) The trait is recessive
b) The trait is dominant
c) no conclusion can be made

In my test I marked B but now that i'm thinking back i'm pretty sure it is C, can someone confirm

>>10172474
god why am i so fucking dumb
now that I am home it is easily C
I don't deserve my brain tissue

If I didnt know that entropy was generated, how would i distinguish an externally, internally, and totally reversible process?

>>10172499
By following the textbook definition of the terms and comparing them to the problem statement. Such things do not exist in the real world.

I need an expression for the length of the red line segment in terms of θ.
The best I've come up with is: [math]min(|sec θ|, |csc θ|)[/math]
I'm sure it can be done better, and I intend to implement this as code.

>>10172805
sec(theta-90degrees)=1/cos(theta-90)
Come on, anon

>>10172839
I know, but I thought using sec and csc would activate people's geometric intuition.

>>10172145
>>10172160
>>10172162
Hello fellow redditor. Welcome to 4channel!

Does abelian just mean commutative?

>>10172929
Basically. Ex: If [math](G,\star)[/math] is an abelian group, then [math]x\star y = y \star x[/math] for all [math]x,y\in G[/math].

>>10172162
>>10172160
>>10172145
>being this autistic about a thread
Stay classy, reddit.

How long does X-ray spectroscopy take to complete? Say for determining the structure of a protein.

Going from a crystallised sample to getting a final structural model of the protein.

I ate some spice food 5 hours ago and just took a burning dump. Is it normal for food to go through your system this fast? Is it different for different kinds of nutrients?

"What percentage is the Gravitational Force from Jupiter, compared to the Force of Gravity from the Sun, on a hypothetical asteroid located at the 2:1 resonance distance?"

Do I just do:

F_g = (GMm)/(r^2) with M being the mass of the Sun and m being the mass of the asteroid and r being the distance from the asteroid to the Sun and then do the same thing but for Jupiter and then compare the two values?

Say you jump as high as you can on Earth, and you end up travelling at 30 ft/s at your maximum speed. If you tried that same jump on the Moon, would your maximum speed still be 30 ft/s?

>>10173811
Just answer two questions:
1) at what point(s) in time of a jump (from and to the same height) is the speed maximal?
2) How (if at all) does the force provided by your legs change with gravity?

>>10173858
1. When you land and immediately after you leave the ground
2. It doesn't?

>>10173900
So, if you exert the same force against the ground, but with less gravity accelerating you downwards (the force of gravity begin less), you know the answer to your original question.

Are we literal walking wave forms?

The Teacher of Ecclesiastes says he found one upright man among a thousand, and not one upright woman among a thousand. How many to have to go to before you find an upright woman? Ten thousand? A million? A hundred quadrillion?

How can I solve y''+sin(x)y=0?
I tried using power series expansions but the product of sinx and y doesn't seem to be too nice to work with

>>10172066
Why do so many people on this board want to kill themselves?

>>10172221
>>10172066
the air you breathe everyday is like 80% nitrogen bro

Is quantum mechanics based on statistical probabilities because the universe is fundamentally random or because our instruments cannot accurately measure at such small scales?

>>10172221
Nitrogen is quite inert gas and as such harmless.
If you halve the amount of non-nitrogen gases in a space, the resulting oxygen consentration drops well bellow life sustaining.
Nitrogen is deadly if mixed with some other basic elements. Nitirc acid amongst the most dangerous. Deadly to inhale even once if consentration high enough, lower consentrations burn lungs most propably leaving you on permanent life support.
To generate gaseous nitric acid is usually a mistake one can't repeat.
Gaseous nitric acid is extremely reactive, to the point of being volatile and most often exotermic, possibly flammable. Reaction with water creates fluid Nitric acid up to 20% consentration in NTP conditions. That is strong enough to "melt" a hole through your hand with 1 drop in few seconds.

Thogh I'm no chemist so take everything with a grain of NaCl.

>>10173142
What is reddit?

Maybe not a sq but more of an industry question; is nanoscience/nanotechnology actually a promising diverse field or is it just creating computer parts? Will it ever become its own industry in the next century?

>>10173858
Is there different terms for the average speed distance traveled over time opposed to average speed in distance of startpoint and end point over time.
What I mean is that you have a point A on say a circle with lenght 1 m. You travel the circle at 1m/s at 1s, 2s, 3s... your difference in position is 0m from the start, but distance traveled increases. So your average speed can be 0m/s or 1m/s.
Speed and velocity?


How many ft in a mile? How many inches in a hop?
How many inch^3 in a gallon? How many rocks does it weigh?
how many ounces in 3.5 rocks?
Who made these insane measurements?

1 inch ~2.55 cm. 1 foot ~.3 m. 1 yard ~ 9.1 m.
1 rock ~ 6.35 kg 1 ounce ~ 28.3 grams

1liter is 10cm^3 and weighs 1kg
1000 meters is 1 km as in k=kilo=1000
1 meter is 100 cm as in centimeter centi=1/100

a tonn of water takes 1m^3 and is 1000kg

>>10174190
How did you come to such conclusion?

>>10174195

This question has a lot of history behind it. My favorite documentary on the topic:
https://www.youtube.com/watch?v=BFvJOZ51tmc

Highly recommended.

>>10172066
> how dangerous is nitrogen? Like if I accidentally flood a room with it and pass out and someone is nearby, do I stand a good chance of being revived?
No, because the nearby person will probably pass out as well. In cases where people die from suffocation or poisoning in an enclosed space, the majority of fatalities (~60%, IIRC) are of people who enter the enclosed space to rescue the first person who didn't come out.

A Russian girl (Maria Chelysheva, if you want to google it) lost her father, mother, brother and grandmother to a cellar containing solanine (a poisonous gas given off by rotten potatoes). The father went down to get potatoes, the others went down looking for the ones who didn't return.

Nitrogen isn't toxic (air is ~80% nitrogen) but it will displace oxygen and cause suffocation. With suffocation involving a build-up of CO2 (e.g. placing a polythene bag over your head), your body detects the excess CO2 levels and induces panic (interestingly, this is about the only thing that can induce panic in people with a defective amygdala, which controls the fight-or-flight mechanism). This doesn't happen with nitrogen: you just pass out and suffocate.

>>10172441
thanks fren

Hey guys, I'm pretty sure I know the answer to this but I would just like to see others opinions. It's a sampling question for statistics.

Question: If we are trying to estimate the number of counties in the US, would it make more sense to use a sample of population count or of land area?

I would assume that land area would make much more sense for this correct? The method would take 10 states randomly with probability proportional to land area.

This would be more accurate than a similar sample of population, right? Mainly due to the large landmass that the US is and how people tend to cluster in a couple large counties.

>>10174882
I'd recommend googling the number, because sampling for available data is stupid.
But area is definitely better. Pick a couple random states, check the number of counties by square mile, average, and estimate based on the whole of the U.S.'s area.

>>10174885
I wouldn't be doing a simple random sample, the states would be randomly selected with probability proportional to the land area of each state. Does this change anything?

>>10174888
Nah.

>>10174892
Great. Thanks anon

I can't wrap my head around this, I want to figure out an equation that works like a parabola.

if X = 1, Y = 1
if X = 5, Y = 5
if X = 10, Y = 1

"X + some magic = Y" for above.

Something like this would be a boon for my video game programming, because as it stands I make something like above work by adding conditions "if X < 5, Y ramp up." and "if X > 5, Y ramps down." I want to figure out some beautiful one-line solution to this.

>>10175077
What exactly do you want the graph of your interpolation to look like? (Draw it).
Of course you can fit a parabola through 3 points, but this is probably not what you want, because this will, in general, lead to oscillations when using more points (look up Runge phenomenon).

You could fit a piecewise spline which would give you the most flexibility.

>>10175077
Option one: polynomial interpolations.
Option two: modular functions. These have some boundaries, but for any n points you have you can make one pass through each.

>>10175091
>modular functions
My bad, I'm retarded.
Things like y=-|x-5.5|+5.5

>>10175088
>>10175096
If you hold down a button, I can make X increase in, say, 0.1 increments as long as you hold that button down. "xThing += 0.1"

What I want to do is make some forward jump move that accelerates into the jump and then decelerates after the top speed and I want it to be centered around holding down that button that increases X. In the event that you release the button, X becomes 0 and everything just stops.

I'll look into all of these things that you guys have suggested.

thanks for your help.

>>10175117
If that's what you want, interpolation works.

>>10175077
A parabola is a quadratic equation: y=a*x^2+b*x+c. Substitute 3 (x,y) pairs (e.g. start, middle, end) and you get 3 equations in 3 unknowns (a,b,c).

E.g. for the values given ((1,1), (5,5), (10,1)), you have:
a+b+c=1 (1)
25*a+5*b+c=5 (2)
100*a+10*b*c=1 (3)

(3)-(1)=>99*a+9*b=0
=> 11*a+b=0
=> b=-11*a (4)

(2)-(1)=>24*a+4*b=4
=> 24*a-44*a=4
=> 20*a=-4
=> a=-1/5 (5)

Substitute into 4
=> b=-11*-1/5=11/5

Substitute into 1
=> -1/5+11/5+c=1
=> c=1+1/5-11/5=-1

=> y=(-1/5)*x^2+(11/5)*x-1

Is there a good, free online database for phase diagrams that has an easy search engine? All that I've found are from random unis or very expensive.

Also, some of the sticky links are now dead

What does relative difference mean in this context? The formula return an approximation but I don't understand what relative difference would have to do with eps

>>10175501
It simply means scaling the absolute difference by some value like the maximum. For example, the relative difference between a million and 999000 would be one in a thousand, or 0.1%

>>10174190
ignore jisatsu threads
ignore jisatsu posters

>be me
>studying economics
>taking linear algebra test
>"invert this three by three matrix"
>no
>do the rest of the test half assed
>get a six
>passing grade here, believe it or not
>do another test
>mostly integration by parts and substitution
>stuff's ridiculously trivial
>literally can't be arsed to double check literally anything
>5
>pass anyway because I got a ten in a previous test which didn't require all that much work
>macroeconomics test
>derive algebraically the Taylor rule
>do all the stuff
>kill me
>get a 3 because I couldn't arse myself
>my grade average is basically 7.8 or close enough
>at home
>study new maths subjects compulsively, pirate books on libgen like I'm insane, solve questions people ask on /sqt/ and here for the fun of it
How do you guys motivate yourselves into getting good grades in painfully boring stuff like multivariable calculus or deriving algebraic rules? Is there a trick to it that I don't know?

>>10171975
So I came across stirling engines the other day and was wondering:

Would a stirling engine that ran off temperature differences between underground (say 7 feet) and outside air be efficient? I wanted to build a small motor to charge my phone

Suppose there is a river and I build a dam on it. Less water will flow through the turbines than the pre-dammed river. That means a reservoir will form. But wouldn't that reservoir just keep building up until it overflowed everything? I know they add spillways, but is the combined water flow of the turbine chute and the spillways equal to the flow if in the pre-dammed river?

Also, why don't they build dams where the entire volume of water is directed towards the turbines?

>>10175595
The efficiency of heat engine depends only on the difference in temperature. The distance doesnt matter. The problem with your idea is the temperature difference underground wont be maintained as heat is dumped into it.

>>10175815
(Volume of water in) - (volume water out) = change in volume of reservoir
This is all you need to figure that out, anon

>>10175861
Why is it change in volume?

How do I get the distance along a hyperbola? Essentially, the "circumference" of the hyperbola. I know hyperbolas are infinite, but I just want a segment of one.

>>10175944
https://en.wikipedia.org/wiki/Arc_length
https://en.wikipedia.org/wiki/Hyperbolic_function

Which one of these do you think looks the coolest?
https://www.strawpoll.me/16944186

>>10171975
Lets say theres a 5% chance ill crash my car driving to work.

I drove to work 10,000 times.

What are the chances that I didn't crash a single time?

Best intro book into game theory? and graph theory? They must be manageable books for a mathlet

>>10175861
>>10175869
Let's assume the flow remains constant. Will the reservoir keep growing?

>>10176251
Dude, just thing about the conservation of mass. For something like water, 1 unit of volume is a fixed quantity of mass. That means there is "conservation of volume" for the reservoir, meaning every bit of volume gained HAS to have flowed in from the river, and every bit of volume lost HAS to have exited by the dam; volume cannot be created or destroyed, only moved.

I don't know how I could make this any more intuitive.

Not that I'm 100% sure I understand this post, but listen to me Dijana Piljak, if these memes are true and you don't kill yourself, you're going to find out about those Bible memes regarding the Lord's wrath. I will feed Ela to starving dogs, and your own child too.

>>10176302
jon tooker confirmed retarded

Inverse Laplace transform
[math]\frac{5s+2}{s^{3}+2s^{2}}[/math]
Partial fractions become
[math]5s+2=\frac{A}{s^{2}}+\frac{B}{s+2}}[/math]
Finishing the equation gives A=1 and B= -2
Thus the answer to the inverse transform should be
[math]t-2e^{-2t}[/math]
but the book says the following, almost the same
[math]2+t-2e^{-2t}[/math]

Where does the 2 come from?

Inverse Laplace transform
[math] \frac{5s+2}{s^{3}+2s^{2}} [/math]
Partial fractions become
[math]5s+2=\frac{A}{s^{2}}+\frac{B}{s+2}} [/math]
Finishing the equation gives A=1 and B= -2
Thus the answer to the inverse transform should be
[math]t-2e^{-2t}[/math]
but the book says the following, almost the same
[math]2+t-2e^{-2t}[/math]

Where does the 2 come from?

Inverse Laplace transform
[math] \frac{5s+2}{s^{3}+2s^{2}} [/math]
Partial fractions become
[math] 5s+2= \frac{A}{s^{2}}+ \frac{B}{s+2} [/math]
Finishing the equation gives A=1 and B= -2
Thus the answer to the inverse transform should be
[math]t-2e^{-2t}[/math]
but the book says the following, almost the same
[math]2+t-2e^{-2t}[/math]

Where does the 2 come from?

>>10176976
Your partial fractions decomposition is incomplete, it is missing the term [math]\frac{C}{s}[/math]. C will be 2.

Something made out of some kind of meme material that can, at least at first, withstand beginning to hit an atmosphere at upwards of 50 or 60 mi/s. What is the effect of atmosphere hitting a craft at that speed when it's as sparse as it is at the very top of the thermosphere? Do materials in contact explode or something or just burn faster? Any weird quantum effects or special stress progression mechanisms or whatever I should know about?

>>10173983
yes

Is there any truth to the ''theory'' that aluminium builds up and gives you cognitive problems over time or is it just pseudoscience and old wives tales?

Is this image correct or am I retarded

>>10177737
Yes

Total noob question here. If I know a line passes through the point (0,0), and I know the angle the line makes with the x-axis, how do I get the equation for the line?

>>10176976
> Partial fractions become
No; the first term has the form (a+b*s)/s^2. In general, the numerator should be a polynomial whose degree is one less than the denominator. It's only a constant if the denominator is linear.

>>10178085
y = x*tan(a)

>>10178085
If theta is the angle,
[math](y-y_0)=tan( \theta )(x-x_0)[/math], where it passes through the point [math](x_0, y_0)[/math]

>>10178096
>>10178095
what if the angle is pi/2

>>10178141
I vertical line through the origin cannot be represented as a function

>>10172145
The only thing that lowers the credibility of /sqt/ is your grammar. Why even leave reddit?

>>10178150
well then how do I graph x=0 in Matlab

can someone explain how this went from the general formula to 252k^2/n^2?
I notice that 252 = 7*6^2 so they squared 6 for some reason but I dont understand why

>>10178341
fuck me nevermind I got it
I wish they'd fucking show intermediate steps or at least mention that they're substituing EVERYTHING

So I'm diagonalizing a matrix, and I finished, but my matrix has the 1,1 and 3,3 entries flipped of what the example has, and I can see that they used a different eigenvector order. My question is does the order matter? Is my diagonal matrix also a valid matrix? Or is there something that I'm missing?

>>10178349
If you your problem tells you that you are working with an ordered basis specifically then the order matters, but otherwise it's fine. The permutations of the eigenvectors in the basis determines what diagonal matrix you get, so there are as many "different" diagonal matrices that are similar to the one you start with as there are permutations of eigenvectors.

i think im misunderstanding pic related.
why is there no case where neither x nor y are in [math] V(G_i) [/math]? also what is the part with 'take the last edge on a path from x to [math] V(G_i) [/math]' about? since we've already assumed the edge's existence in the case, right?

>>10178163
You don't.
>>10178349
Sure is. If you don't believe me, try for some random vectors.

>>10178411
>>10178426
Oh ok, thanks.

>>10178341
>>10178343
nevermind one more time
Im supposed to find the formula of a right hand riemann sum on y=4x
I can do this perfectly fine when the starting contour is 0 (and thus the 'a' in the general equation goes away) but I cant do shit when its not
Im supposed to be getting 16 + 8/n for the second one but i keep getting 8 + 16/n
any idea what im doing wrong, because Ive got none

Please help me sci I'm trying to learn math on khan academy and I'm having a road block on exponential expressions

Right now I'm trying to wrap my head around how ie: (1/7)^x/(1/7)^2 turns into 49×(1/7)^2. I guess I'm falling to understand how 1/7 squared turns into a whole number, wouldn't it be 1/49 or 1^2/7^2?

>>10178939
Are you sure it wasn't x = -2 rather than x = 2. because 1/7^-2 = 49. since (7^-1)^(-2) = 7^[(-1)(-2)] = 7^2

>>10178939
The expression you posted turns into 49(1/7)^x, not to the power of 2.
You are correct that (1/7)^2 = 1/49, but this is in the denominator of the fraction. So 1/(1/49) = 49.

>>10178954
My bad, I meant to the xth power not squared there. And I think I just realized what I was forgetting, I'm an idiot. (1/7)^x/(1/49) is the same as multiplying by the reciprocal. Whoops

Does this actually work?

Sometimes it feels like my brain doesn't connect the dots on things, other times it does.

Any nootropics that'll help?

>inb4 eat healthy and exercise
already do, I want to transcend my mental capacity

>>10179472
Nootropics don't work.

t. someone who tried every nootropic and then got addicted to research chemical stimulants. Just stay away.

>>10178555
looks fine to me. Maybe they got it wrong.

>>10179507
that's unfortunate to hear
thanks for the warning, take care anon

I have a table of every team in the MLB matched with the total number of homeruns that the team has hit. There are 30 teams in mlb. Using this table, I'm supposed to calculate the probability that the Red Sox and Dodgers are selected for a random sample of size 2. This sounds basic but I don't want to get it wrong. It should be 1/30 + 1/29 right?

>>10179691
product, not sum. Also you forgot the reverse pairing, so the probability is 2/30/29.

Maybe a simpler view: 30 choose 2 = 15*29 possible pairings (unordered). One of them is the one you want.

>>10179706
So the calculation would be (1/2)*(1/30)*(1/29)?

>>10179709
No...
1/30 times 1/29 is the probability that the random pairing is (redsox,dodgers). (dodgers,redsox) is chosen with the same probability.

>>10179722
Ok, thanks man. I'm trying to teach myself this stuff from a book and it's just kinda messing with me rn.

>>10175590
lmao brainlet needs to be motivated in order to do something

Anyone have that screencap about the history of wave physics and how the math behind it was discovered earlier and was purely theoreticak but nobody found a use for it until discovering waves?

Why don't we know why a proton weighs more than an electron? Can't we just look at what's inside and keep going deeper?

>>10180579
Without going further, we know that a proton weighs more than an electron from experiments done on both particles. It takes more energy to accelerate a proton than an electron and that's that. Why something happens in physics is only relevant to the fundamental aspects you are going to assume as true because the experiment says so. Tha's an empirical limit that you have to accept in any scientific field. For all we know the electron is a fundamental particle. so it's physical properties DEFINE that particle. And while you can ponder that certain physical properties come from other sources, you still are going to reach a fundamental aspect that you have to take as a sort of axiom. Then it's all philosophy, and while there is interesting discussion within it, it makes no sense to argue the point through empirical means.

If x is function of y and y is also function on x, what do you call this relationship? Is it like a mutual function, double function, or what?

>>10181174
A bijective function?

>>10181174
It's this>>10181190 or an invertible function.

>>10181194
Those two mean the same thing.

DO THEY MEAN -(X^2) OR (-X)^2
FUCKING PLEASE
TELL ME

>>10181406
the first one

>>10181406
either the guy who wrote that is a retard and meant (-x)^2=x^2 which makes the sign pointless. or you are the retard and it's -(x^2)

>>10181410
THANK YOU
>>10181411
Im stupid, thats why I'm in /sqt/

>>10181415
There's always the possibility that the guy who wrote that is a retard.

>>10181421
it's mymathlab so you might be right

If I attach illegally downloaded (from sci-hub) paper files to document entries in Mendeley and then sync them, will I be banned?

Whats the point of "virtual work"? Why do they have to be "virtual/imaginary/mathematical" displacements, and not just, you know, "displacements"? Is it just a way of saying "we're dealing with a static problem, so there shouldn't be any movement", so it doesn't really matter in the end?

>>10181497
no

>>10171975
>if p is a prime >5, then p^2 mod 30 equals either 1 or 19
i am stuck. tried both of the ways described here:
https://www.youtube.com/watch?v=ZMkIiFs35HQ
tried case by case for every remainder of division by 30
1 => last digit of p^2 must be one, it is either a multiple of x1 where x is adequate or a prime, but prime canot be a square, so p is a prime
2, 4, 6, 8... 28 => implies p^2 divisible by 2, therefore not possible
3 => no number multiplied by itself from 0-9 gives a number which last digit is 3, therefore not possible
5 => implies p^2 divisible by 5, not possible
7=> wlog like 3
9=> p^2 is (some number divisible by 30 )+ 9.
digits of p^2- 9 should add up to n, divisible by 3, so sum digits of p^2 is divisible by 3. stuck
11 => last digit of p^2 is 1. therefore last digit of p must be 1. stuck
13 => like with 3.
15=> like with 5
17=> like with 7.
19=> i do not really know
21=> same as 19
23=> same as 3
25=> same as 5,
27=> stuck
29=> stuck.

>>10182598
p is a prime>5 if and only if it's coprime with 30.

>>10182605
My bad, no only if.

>>10182608
I'm an idiot, the only if is true, the if isn't.

Can someone help me solve this ODE?
ty' + y + ln(t) = 0
First we isolate (Eh) which is ty' + y = 0 <=> ty' = -y so y' = 1/t * (-y)
How do I find the primitive of 1/t * (-y)? I really suck at integrating things.

>>10182638
Integration by parts.

>>10182645
Actually nigga what is t, is it the variable for y or is it just a random constant?

>>10182645
>>10182646
t should be the variable, the question is badly written but I assume I'm trying to find y(t).

>>10182638
>>10182650
Watch this:
[math]ty’ + y + ln(t) = 0 \Leftrightarrow ty’ + y = ln(t)[/math].
If you squint a bit, you see that [math] ty’ + y = (ty)’ [/math]. Now you just need to integrate both sides:
[math] \int (ty)’ \mathrm{d}y = ty = \int \ln(t) \mathrm{d}t[/math]. The integral on the right is [math]t(\ln(t)-1) + C[/math]. I’ll leave you to find y by dividing through by t on both sides.

>>10182674
I’m sorry, missed typing the negative sign on the right. So it is of course [math] ty = t(1 - \ln(t)) + C [/math].
Finally, [math] y = 1 - \ln(t) + \frac{C}{t} [/math]

>>10182674
Thank you, I understand the entire process but
>ty+y=(ty)
What's the reason for this? I mean, how do you get that result.

>>10182687
ty+y is not ty. ty' + y = (ty)'
To see that, differentiate f(t) = ty using the product rule.

>>10182699
Yeah I meant (ty)'. Thanks again.

>>10182701
I didn't answer your question. The general process is called using an integrating factor, for ODEs of the form y' + f(t)y = g(t). If you can find a factor u(t) so that uy' +fuy = (uy)', you can multiply the equation with u(t) and simply integrate both sides. Finding u is accomplished by solving u' = fu.

>>10172347
Because you can’t go back in time

So I clean my dry herb vape pen with isopropyl alcohol and changed the coil to a brand new one and then it knocked me flat on my ass after just one hit. Usually it's two or three hits just to a get a moderate high. Can someone help me understand this?

How does on do rotations on AVL Trees?

any smart people want to help me with this? It's been haunting my dreams for over a week now.

Have a problem with understanding finding vector x in the following case:


[math] A=
\left[ {\begin{array}{cc}
2 & -4\\
-1 & 2\\
\end{array} } \right] \left[ {\begin{array}{c}
x_{1}\\
x_{2}\\
\end{array} } \right][/math]
[math]v=[-6\,3][/math]

After applying Gaussian elimination to the system of equations I get the following equation
[math]x_{1}=-3+2x_{2}[/math]
And the answer according to the book is:
[math]x=[-3 \, 0]^{T}+x_{2}[2 \, 1]^{T}[/math]
cba to make vertical vectors in tex again so just using transposed vectors

And of course my equation got the -3 and 2 in it, but I have no clue how to form those vectors otherwise. Like where does the 0 and 1 come from that equation?

>>10183206
a fuck should have used more \, to indicate space
just read [-6, 3], [-3, 0] and [2, 1]

>>10183206
>>10183207
A matrix is also singular so can't find inverse matrix

>>10183111
What's [n]? Is it the set S that contains every natural smaller than or equal to n?
If that's it, I'd think about in term of non-repeating aditions. So that for 1, you can add nothing for all k, or you can add 1 in one k, so we have 2k.

>>10183211
Yeah, n = {1,2,3,...,n}

The way I'm thinking about it so far is this the creation of sets at each list choice.
First item in list: Any subset from [n] which is 2^n.
Second item onward: Can add from the remaining elements.

So like, if n = 4, and we want k = 2:
Item 1: {1,2,3}
Item 2: (Since 1,2, and 3 are already in the previous list, we can add nothing or 4}
Item 3: (If item 2 added nothing we have nothing or 4 again, if 4 was added in item 2, we can only add nothing)

>>10183263
Hm, that's right. But we can formalize it better.
If for n, there are so many ways of dividing the set into say, l parts, as l goes from 1 to n-1.
Associated to each partition of the set in l is a permutation, as you add piece by piece of the set, and also empty sets.
You should be able to solve the individual parts, and adding it all up is easy.

>>10180454
respond to this

>>10183206
From [math]x_1-2x_2=-3[/math] you know that all points on that line satisfy the equation. The point [math]\pmatrix{-3 \\ 0}[/math] is just one choice. [math]\pmatrix{-1 \\ 1}[/math] is another.
The solution in your book is just a parametrization of this line.

I am having issues with the integration to prove its normalized where int_-a^a psy dx =0 an the |psy|^2dx malarcky. Anyone able to help me?

How does this guy go from (5) to (6)?

https://www.eventheevens.com/textbooks/8/introduction_to_quantum_mechanics_2nd/problems/339

What would be an ideal textbook to self study for special and general relativity?

>>10183521
You should get a gaussian integral for the normalization. What exactly do you need help with?

>>10184108
It's just applying the product rule for derivatives in reverse.

>>10171975
Can someone please provide link to that mensa iq test people always post screenshots of here?
Cant find it.

>>10184108
>>10184108
nice website

>can write semi-functional things in C++
>crush multivariable calculus courses
I'm obviously not dumb so why can't I understand linear algebra? this is the most unintuitive bullshit ever god damn fuck matrices

>>10184485
matrices are good for when you want to examine more than one of something. Often times one observes the most important features of a facet with scalars

>>10172929
Yes. Abelian is just named after a guy called Abel, who I imagine studied some commutative shit.

>>10184485
yeah, im much the same. I also hate geometry, but this shit just seems so convoluted. Since you're smart you might just be able to study through it if you really double down and have it start to make more sense with more examples, i read up a little more and kept rereading and it slowly started seeming less alien

>>10183063
There's less gunk blocking the screen so more stuff can get through...

>>10184485
>>10184709
Linear algebra is very intuitive once you start thinking about matrices as linear transformations. Watch 3blue1brown’s Essence of Linear Algebra series for the right intuition.

Is there a good scientific python book for python 3?
The wiki's recommended books are for python 2

>Struggling to solve simple circuits
>Can't even begin to understand AC circuits
>Exam is a month from now
Give me strength, /sqt/

Is it a rule that you never want to write a fraction with complex denominators and should always multiply the fraction with the complementary complex number?

>>10185099
Yes, because division in complex numbers is weird.

>>10185100
alright, that makes the answer more sense

>>10185099
You ideally want to write complex numbers in a form where the real and imaginary parts are both explicit, i.e. a+bi where a and b are real. But if a and b are both fractions with a common denominator, then (a+bi)/c is basically just a compact representation of (a/c)+(b/c)i.

>>10185085
Show an example problem and we'll try to see why you struggle. You probably need to work on some intuition. It's possible to fix in your timeframe. Try not to spend time worrying.

I have the following problem
I am trying to solve a differentialequation system with eigenvalues:
[math]x_{1}'=x_{1}+2x_{2}[/math]
[math]x_{2}'=-x_{1}+3x_{2}[/math]
[math]x_{1}(0)=0, x_{2}(0)=1[/math]
Then the eigenvalues will be 2+-i and eigenvectors [1+-i, 1]
The problem is, I don't see how I can get the answer here according to the book:
[math]x_{1}=2e^{2t}sin(t)[/math]
[math]x_{2}=e^{2t}(sin(t)+cos(t)[/math]
I know that the template of a complex solution to a differential equation has cos and sin in but I am still confused how I am supposed to multiply the eigenvectors into this.

I have the following problem
I am trying to solve a differentialequation system with eigenvalues:
[math]x_{1}'=x_{1}+2x_{2}[/math]
[math]x_{2}'=-x_{1}+3x_{2}[/math]
[math]x_{1}(0)=0, x_{2}(0)=1[/math]
Then the eigenvalues will be 2+-i and eigenvectors [1+-i, 1]
The problem is, I don't see how I can get the answer here according to the book:
[math]x_{1}=2e^{2t}sin(t)[/math]
[math]x_{2}=e^{2t}(sin(t)+cos(t))[/math]
I know that the template of a complex solution to a differential equation has cos and sin in but I am still confused how I am supposed to multiply the eigenvectors into this.

I have the following problem
I am trying to solve a differentialequation system with eigenvalues:
[math]x_{1}'=x_{1}+2x_{2}[/math]
[math]x_{2}'=-x_{1}+3x_{2}[/math]
[math]x_{1}(0)=0, x_{2}(0)=1[/math]
Then the eigenvalues will be 2+-i and eigenvectors [1+-i, 1]
The problem is, I don't see how I can get the answer here according to the book:
[math]x_{1} = 2e^{2t}sin(t)[/math]
[math] x_{2} = e^{2t}( sin(t)+cos(t) ) [/math]
I know that the template of a complex solution to a differential equation has cos and sin in but I am still confused how I am supposed to multiply the eigenvectors into this.

say
[math] e^{2t}(Acos(t)+Bsin(t) \cdot [1-i, 1] [/math]
[math] e^{2t}(Acos(t)+Bsin(t) \cdot [1+i, 1] [/math]
this will give the following(ignoring A and B):
[math] cos(t)-icos(t)-isin(t)+sin(t)[/math]
[math] cos(t) + sin(t) [/math]

and

[math] cos(t)+icos(t)+isin(t)-sin(t)[/math]
[math] cos(t)+sin(t) [/math]

adding these together gives the following
[math] Acos(t) [/math]
[math] Acos(t)+Bsin(t) [/math]
I must surely be doing something wrong, right?

>>10185085
Ac single-phase circuits are exactly the same as DC circuits but you work with phasors instead of normal numbers.
They're actually easier as if you have any energy storing components (such as capacitors or inductors) they can be modeled as a complex impedance instead of as a function of time that needs to be transformed to its frequency domain equivalent.
Note that regardless of what youre dealing with you will always use the same tools, namely Thevenins theorem and kirchhoffs laws.
I highly suggest you get yourself a copy of Matthew Sadikus' fundamentals of electrical circuits, its probably the best introductory book on the subject and most likely is the one being used by your teacher. Its also very good for self learning as it does convey everything as simply as possible.
As a last note id really wouldn't stress about it, circuits aint the hardest thing out there and there are tons and tons of resources out there on the subject, you also have more than enough time to take a significant grasp on the subject.
Dont stress it bro, just get to it.

>>10185179
solve the different eigenvalue equations like
x'=(2+i)x
-> x=e^2t*e^-it
and do the usual stuff

I took the WISC test as a kid. My scores were never shared with me until now, and apparently, while I'm pretty average in spatial and processing, I am at genius level in verbal comprehension and fluid reasoning.

What sort of careers is that good for? I've always been very good at languages, but I find the idea of just being an interpreter kind of unappealing.

>>10185255
literally nothing. Only performance IQ matters

>>10184464
>>10183521
I dont know how to integrate it.

>>10185179
>>10185193
Is it possible you didn't look at the initial condition? The general solution is
[math]x(t) = C_1 e^{(2+i)t}\pmatrix{1+i \\ 1} + C_2 e^{(2+i)t}\pmatrix{1-i\\1}[/math].
So [math]x(0) = \pmatrix{ C_1+C_2 + i (C_1-C_2) \\ C_1 + C_2 } = \pmatrix{0 \\ 1}[/math]

You'll get [math]C_1 = 1/2 + i[/math], if you now multiply the stuff out and write all complex numbers in polar form you'll probably encounter the phase shift that sends your trigonometric functions pi/2 to the side, that's why sin and cos are the other way around from what you thought.

Ok, let's say that there is a social study that shows a correlation between two variables.
Which studies are required to know if the relation is causation or not?

>>10185288
Well, I'd suggest looking up a gaussian integral, then. They show up all the time, and it's definitely worth knowing. It's a well-known fact that the indefinite integral is not expressible in terms of elementary functions. On the other hand, the total integral is pretty straightforward to calculate: square the whole integral, rewrite that as a double integral, and then go to spherical coordinates.

>>10185571
*polar coordinates

are there any simple way to find solution for a cubic equation=0? I was never taught that in class other than very anecdotal cases where I should look at the last number, eg if the last number is -2, then it must be (x-2)(x-1)(x-1)

>>10185724
There's a formula but it isn't simple

>>10185736
o fuk, so if I am at exam and is required to find the eigenvalues of a 3x3 matrix, I am pretty screwed right? There was one task that was basically impossible with my knowledge to solve to find the solution for x for a cubic equation and I had to use an online calculator

>>10185748
say this one
[math] x^{3}-4x^{2}+5x-2 [/math]
Here the only way I managed to solve it was to assume that the last part could only have 1 solution:
>all x must be positive as -x*-x*-x=-x
>the terms could be no higher than 2
>as one term has 2 in it, the others MUST be 1
thus I figures out it could be (x-2)(x-1)(x-1) which was correct. But let's say the last number is -12. Then wtf?? Could it be (x-3)(x-2)^2 or could there be other answers?

>>10185762
or what if the last number is positive? Then it's pure guess which x solution could be negative

>>10185724
>>10185762
>>10185765

Depends on what kinds of expressions they are, and what you mean by simple. There are explicit solution formulas for the roots of a cubic (google Cardano).
If you're sitting in front of a piece of paper, it is often simplest to guess a root and factor it out. For this, the best way is Horner's method.

For example, let's try finding the roots of [math]3x^3+7x^2+5x+1[/math]. All integer roots divide the constant term, 1 in this case, but 1 is not a root; -1 is (You can also check for this by comparing the sum of coefficients of even powers with the sum of coefficients for odd powers; if they are the same, -1 is a root.
So you split off that root to get (x+1)(3x^2+4x+1).

These are the steps you should keep in mind for those kinds of exam questions:
- sum of coefficients is zero => 1 is a root
- sum of even coefficients = sum of odd coefficients => -1 is a root
- in a polynomial with constant term, all integer roots divide this constant
> But let's say the last number is -12
Then you check 1, -1, 2, -2, 3, -3, 4, -4, 6, -6

>>10185762
>But let's say the last number is -12. Then wtf?? Could it be (x-3)(x-2)^2 or could there be other answers?
It could be (x + a)(x + b)(x + c) for any a,b,c such that a*b*c = 12. e.g. a=-12, b = c = 1, or a=12, b= c = -1, or a = b = 3^(1/2), c = -4, etc, so infinitely many solutions. You should do it like >>10185783 said and just check small integers, then after finding the first root, use polynomial division and the p-q-formula. You know about polynomial division, right?

>>10185860
P-Q formula, I e only heard continental Euros use that term.

Why is Pluto so cold when it's getting the same amount of energy from the sun as the earth? How the fuck does a goldilocks zone even exist?

>>10186188
>it's getting the same amount of energy from the sun as the earth?
Ask me how I know that you're retarded

>>10186188
Never mind. I guess inverse square law also applies to stars. I thought it was because in an atmosphere light had to travel through more stuff but it's actually because the radius grows larger which disperses the photons...

Plsplspls help me i am retarded (not underaged). So, how do I know which direction of domain and range arrows i should use? For example, (-5,0) = -5, —> and 0, <—
Why does 0 have a left pointing arrow and why does -5 have a right pointing arrow?
Pls help me you’ll save my life.

I'm confused about part b, for a Poisson process is the CDF the product of their individual Poisson random variables, or its sum?

Question, if h(n, k) = h(5, 2), does the algorithm even terminate? I must be doing the box trace wrong since the gap between n and k gets exponentially larger

Can anyone identify this Rock for me? A quick google search says it might be meteorite slag or fulgurite, but I'm not sure.

Found it on a beach, this is one of the smaller samples I found washed up. Some were about the size of a persons head.
This one doesn't react to magnets. It looks partially melted.

If inbred organisms are more likely to mutate, does this make their population prone to faster evolution?

>>10186808
The arrows point to where the set goes from the point. In your example it goes up from -5 so its points positively while it goes down from 0 and so points negatively.

But really i'm just disgusted by this rape of interval notation which is some of the best and most intuitive notation in math.

>>10187523
Genetic mutations/conditions are more likely to travel and spread through smaller, more genetically isolated populations.
Its the isolation thats the main factor there, the inbreeding is a seperate thing, it just doubles down on those conditions and mutations, cements them into the population.

>>10187126
so show your attempt and we will tell you the fault in your reasoning.
h(5,2)=h4,1 + h4,2=4+h3,1+h3,2=7+h2,1+h2,2=10

how the fuck do I solve cubic equations like these without calculator
[math] -x^{3}+5x^{2}+7x-6=0 [/math]
pls help, I might get shit like this on exam

I like science and engineering and i’m bretty gud at maths but I hate humankind.

I don’t want a career in STEM if it means I make things better for humankind. Surely there’s some careers where I work against humankind, like weapons development?

>>10188199
Use horner‘s method, and follow the steps outlined in >>10185783.

The fuck do I do with my university holidays except work, shitpost and vidya? What do normies do?

>>10188582
I'm reading up on Sakai's Geometric Aspects of General Topology, then I'm going for Loukas's Classic Fourier Analysis. If there's remaining time, I've also stolen a book on Riemannian Geometry.
Other than that, visiting family, watching Index 3 and Jojo.

>>10188604
I asked on red*it if there were any anki decks I could study in my field and they basically told me to fuck off. My course is full of gunners and the job market is shit so I should probably find something to do.

>>10188622
What's your course?

>>10188649
medical radiations

Someone please explain constellations to me. I just don't see it. None of these look even remotely like the things they're named after. Worse, you can "connect" the stars in a million alternative and equally (im)plausible ways, and they would still resemble nothing.

So 1) how and why the fuck did the dead fuckers from thousands of years ago come up with this shit and 2) why do we continue to use them? Just erase them from the public record and common usage and put them in the box of disregarded dumb stuff, along with alchemy and humours etc.

Assuming this is the stupid question thread...how the fuck do I do this.

>>10189136
1)They liked looking at the stars a lot and had a fair share of mystic and divinatory traditions. When it became scientific, those constellations were the most consistent and standardized way to discuss astronomy, which is why the first catalogs used them,

2) A simple look at modern star catalogs shows you how difficult it would be to conceptualize the stars with a perfectly logical catalog. So while computers can sift through all the numbers and letters, its still easier from average people and astronomers to call the star closest to us Proxima Centauri.

>>10171975
Anyone know why the rates of reaction are changing? I guess it has some to do with the cycloring size and strain

[math]M=\frac{2Q^{2}}{\sqrt{4Q^{2}+1}}[/math] Can I turn this into a Q = f(M) equation? I squared it and split it into two polynomial fractions because it was the only thing I could think of, but it didn't get me anywhere

>>10190098
Quadratic formula.

>>10190127
fuck

Is there a difference between an agonist-antagonist and a partial agonist or are they one and the same? If yes what?

>>10190080
Ez. SN2 needs back side attack. 6 member rings > 5 member > 4 > 3 in terms of space available for the :Nu to approach. So it's cause of steric hinderance.

>>10190080
Increases in steric hindrance against sn2 nucleophilic attack slows down the reaction considerably.

How do I solve for a mass in units of 10^11 solar mass

>>10190422
Figured it out. Bitch gave the notes wrong. Was looking at pentazocine which is a mu opioid antagonist & kappa opioid agonist. She had it down as "can activate the receptor on its own but also blocks the access of more powerful drugs to receptor"

I'm trying to show that [math]f:P(N) \to R[/math] by [math]f(A) = \sum_{j \in A} 3^{-j}[/math] is an injection. Is there a nice, clean way to show this? Everything I come up with is nasty.

Here's an attempt. Say [math]A,B \in P(N)[/math] with [math]A \neq B[/math]. Let [math](A \setminus B) \cup (B \setminus A) = \{m_0 < \dots < m_k\}[/math] (WLOG assume [math]m_k \in A[/math]). Then [eqn] 3^{m_k} |f(A) - f(B)| = | 1 + (-1)^p (3^{m_k-m_{k-1}}) N| > 0[/eqn] where [math]p \in \{0,1\}[/math] and [math]N[/math] is some messy sum of positive powers of three. In any case [math]|f(A)-f(B)| > 0 [/math].

I’m thinking of switching from EEE to Applied Maths. Can AM majors work in pretty much every industry including energy? And will the coursework be lower?

>>10190849
Maybe you can use that the number representation in any base is unique?

can anyone prove this?
() stands for the combination.
much thanks.

>>10191171
What have you tried?

When making a full linear model, how can I tell which predictor should be second order (Quadratic) and which shouldn't be? I'm using R.

>>10191188
Tested on n=1,2,3,4 and it worked, but I don't have a clue how to prove it.

>>10191222
Did you try expanding the combinations and algebraing your way?

Biased and Heteroscedastic?

>>10191232
Yes, but I don't see any significant progress. I wish I could take a picture of my work and post it but I can't at the moment.

Say you jump as high as you can on Earth, and you end up travelling at 30 ft/s at your maximum speed. If you tried that same jump on the Moon, would your maximum speed still be 30 ft/s?

>>10191171
[eqn] \int (1 + x)^{2n} = \sum \int \binom{2n}{2n - k}x^{2n - k} [/eqn]
[eqn] \frac{(1 + x)^{2n + 1}}{2n + 1} = \sum \binom{2n}{2n - k}\frac{x^{2n -k + 1}}{2n - k + 1} [/eqn]
and
[eqn] (1 + x)^{n} = \sum \binom{n}{k}x^{k} [/eqn]
Now the LHS is easily seen to be the coefficient of [math] x^{2n + 1} [/math] in [math] (1 + x)^{2n + 1} (1 + x)^n /(2n + 1) [/math] which is just [math] \binom{3n + 1}{n}/(2n + 1) [/math]. QED

>>10191241
performing log(y) to all Y values gave me this outcome. This is a better model at face value, right ? The Q-Q is perfectly linear now.

>>10191246
wow, thanks a lot! :)

>>10174190
natural 4chan user behavior

>>10191244
Why do you keep posting this?

>>10191409
>Using "brainlet" images
He clearly doesn't know any better

>>10191440
The question reminds me of this story.
http://www.phys.ufl.edu/~det/phy2060/heavyboots.html

>>10191469
>73% got it right
>27% got it wrong
>Of which 33% chose heavy boots
>Followed closely by safety ropes at 27%
>Almost half of the people got the other question wrong
Pfffhohohohohohehehehehehe

Why is dropping all insignificant predictors from a model in one step a bad idea?

How do i solve:
cos(x)*e^sin(x) - sin(x)*e^cos(x) = 0
With x ranging in [0,2π]

Do engineers have a complex about majors?

I'm an applied math major, 1 of 2 in a room of 30+ electrical/mechanical/(insert here) engineers. I have never talked to one of them till today for a group project on designing a sustainable university campus.

This mechanical engineer was shitting on me the whole day. "Oh, you're an applied math major. Why? There's no jobs out there for you (haha)". "Oh, you don't even know what a "technical term" board is? (haha)".

I'm just trying to pass man. What the heck just happened.

>>10191763
Maybe they're insecure. We had separated classes for physics and biology in highschool so I landed with all the other guys that mostly studied engineering and they were mostly a bunch of betas that would do everything that was normie and geeky but wouldn't care about anything really advanced and didn't have autism, always talking about finding jobs or some normie shit

>>10191699
You can try using these identities

>>10191781
>>10191699
Do you even need to use those?
It's pretty obvious that it's 0 at and only at the points where cos(x) and sin(x) are the same

>>10191795
Not solving it analytically is boring tho

>>10191409
I want someone to come out and tell me the answer because I'm literally retarded. I keep getting questions as a response to my question.

>>10191244
>of course it w-
>but you'll leave the ground faster, so you'll apply less force
>o-oh, so it isn't actually trivial, lemme model it properly
When you jump, first press your legs up together, and then you expand. Your feet touch the ground the whole process, so that you'll be applying the jump's force along the height difference between crouching and standing.
Because the gravitational force in earth is higher, the jump on the moon produces more work (the more final force along the same distance), and thus speed.

>Prove that either 2 · 10500 + 15 or 2 · 10500 + 16 is not a perfect square.

How the fuck do i get good at proofs? And here I thought I was not a brainlet cause I made it through calc 1-4...

>>10192778
Th-that's a question where you pick which one you want to solve, right? Th-there's no way they want you to prove the or, right?
You know, those numbers are small enough I'm tempted to literally do it manually for the jokes.

>>10192778
I'm guessing that your \cdot means 'to the power of'..
see https://math.stackexchange.com/questions/595149/prove-that-either-210500-15-or-210500-16-is-not-a-perfect-squa

>>10192788
no it means multiply. I copied and pasted from a PDF

>>10192778
>>10192787
I think it means one or the other is guranteed to be right.

>>10192815
Well, the same ideas apply. n^2 and (n+1)^2 are 2n+1 apart, so the only consecutive squares are 0 and 1.

>>10192819
Neither is right.
t. my calculator

When talking about the speed of sound in air, liquid, solid, or whatever, is the speed given the maximum speed at which the waves travel ? Or do they always travel at the same, constant speed ?

does anyone know what he means by the top definition? Like, what are the elements? Is that the symbol for elements in a product, or disjoint union, or just elements of the stalk in general? I can't seem to make it out given that the only other definition I found on the internet was that thing that doesn't look too similar.

>>10193033
The same constant speed. You can try it by throwing a rock really hard into the water at one end of a pool, and simply dropping it in the water at the other end of the pool at the same time. the waves should reach each other in the middle of the pool, meaning the speed at which waves travel through a medium is constant.

>>10193045
I see. So I'm guessing that the only difference in the sound wave of say a cough and an explosion is the pressure variation of the wave and not the speed ?

>>10193049
Right. Have you ever been to a baseball game? If you sit very far away from the batter, you can see the ball fly away before you hear the bat hit. The same goes for an explosion: if the batter gets blown up by dynamite, you're still going to see the explosion before you hear it.

>>10192778
the question is misleading, since the numbers themselves dont actually matter here, any 2 consecutive positive numbers cant be both squares.
like >>10192831 said

some proofs are nearly black magic, other proofs you can do on your own just through practicing others

>>10193064
> Have you ever been to a baseball game?
No, but I've seen fireworks and thunder, I know how this works.
What I have trouble understanding is how vastly different amout of energy can result in something travelling at the same speed, especially on the lower side of things.
I get that the speed of sound can be limited by the element in which it is travelling, but I still don't get how even the quietest sound will still result in a wave travelling at 340m/s

>>10171975
> Given a mass balance, find the energy balance.
I have this giant table in which there are elements and compounds.
Each of them has H (kcal / mol), S (cal / (mol * K)) and Cp (cal / (mol * K)) in the constants A, B, C and D (an equation that relates Cp and its constants) and all the above in various temperature ranges (H, S, A, B, C, D for T1 to T2, H, S, A, B, C, D for T2 to T3, etc.).
A list of reactions.
A list of input elements and compounds ... and another output
All inputs, reactions and outputs have their given mass.
Some compounds and elements enter the Temperature T_in1, others to T_in2 and so on.
The same for the exit (some go to T_out 1, others to T_out 2 ...)
> Calculate the energy balance, constant pressure
My question is what happens to the elements or compounds that do not react, for example, N2 (does not appear in any reaction), if we take an input temperature of 273.15 K and a higher output (398.15 K for example)), So I only calculate the "sensible heat" to N2 by integrating the Cp with its constants?
And the compounds that do not react?
The enthalpy of reaction, I calculate from the table at 298.15 K right?

should I be concerned that the specific program I'm going into at an accredited university is not accredited? they have several accredited degree programs but the one I'm looking at is not on the list (though they obviously offer the degree)

>>10193429
yes

I’m trying to make a list of CB-1 inverse agonists and came across the term covalent inverse agonist (for falcarinol)

In my 10 minutes of googling i can’t figure out what covalence means for receptor antagonists (only when irreversible agonists bond permanently through covalent bonds).
Any help would be much appreciated.

>>10191781
What if we aren't allowed to use complex numbers in this course?

>>10191795
But how can you be sure that other points don't exist?

>>10191781
> But how can you be sure
Use the identity [math]A\cos x + B\sin x = C\cos(x-\varphi)[/math], with [math]C=\sqrt{A^2+B^2}[/math] and [math]\tan \varphi = \frac{B}{A}[/math].
So, [eqn]\cos(x) e^{\sin x} - \sin(x) e^{\cos x} = \sqrt{e^{2\cos x}+e^{2\sin x}}\cos(x-\arctan(-e^{\cos x - \sin x}))[/eqn]

So I got in an argument with my friend today. He says that "light speed is useless because if we wanted to travel to another galaxy, we would be dead before we reached it". However, I said that "at the speed of light, time and distance converge to instantaneous travel and that we wouldn't age. However everyone else going at regular speed would be long dead" am I right or wrong?

How would you rearrange to find 1 unknown Mass?

Help a brainlet out

>>10194718
1) get everything that is a product of m_1 on one side of the equation and everything else on the other.
2) factor out m_1
3) divide out the non m_1 part

>>10194736
it just works

the church of Scientology website says that "The pictures in the mind contain energy and mass." Could this statement be interpreted as true somehow? Would it be possible to measure them?

How can I prove that a real sequence that diverges to (positive) infinite is eventually increasing? I'm thinking about contradiction but I can't get anything

>>10194736
my answer doesnt make sense though

m_1 (a bus) was the same as m_2 (a car) but negative

in the question it says the bus collides with a car both travelling at the same speed in opposite directions. They both stick and the bus carries on in the same direction but at a lower speed.

>>10194772
[If you can't read the stuff between the math tags then turn off your adblock]

What is your definition diverges and eventually increasing? Because this result is not true for the standard definition of diverging:
Consider the sequence [math]x_n = n[/math] if [math]n[/math] is even and [math]x_n=0[/math] otherwise. Then this sequence diverges (that is, there are arbitrarily large terms) but is never eventually increasing because you always have a term at 0.

If you mean "a real sequence [math]\{x_n\}[/math] that *converges* to positive infinity", if you include infinity into the extended real numbers, then you can argue as follows:

Converging to infinity implies that [math]\lim x_n=\limsup x_n = \liminf x_n =\infty[/math]. If you don't know what the latter two are it's very simple. It basically means "when you cut off the tail of the sequence at some n, look at the sup or inf of the remaining terms, then let n tend to infinity".

Now suppose that the sequence is not eventually increasing. Equivalently, there is a subsequence [math]y_m[/math] that is not increasing, and hence has an upper bound [math]y_m\leq M[/math]. Then [math]\liminf x_n \leq \liminf y_m\leq M[/math], contradicting [math]\liminf x_n =\infty[/math].

>Go to /sqt/ because dont understand problem
>Been skipping my Astronomy class sometimes
>No one replies to my question so I delete it
>Figure out the equation and answer
>Even the Professor is stumped
>No one else seems to have solved it
>Professor sees I am the only one who got it right
>Explain to Professor how to correctly get the equation
>Find out I have the top grade in the class
>Despite skipping a good chunk of the classes or falling asleep sometimes
>Am a comp sci major and was thinking of dropping out of university

Feelsgoodman

On an AC circuit, if I'm told that the total current is 0.3, what is the phase angle of said current? Is it 0? Is it unknown?

>>10194815
I don't understand your difficulty. If the speeds are the same magnitude before the collision, u_1 = -u_2. The equation reads
[math]\frac{m_1-m_2}{m_1+m_2}u_1 = v[/math]. Or [math](u_1-v)m_1 = (u_1+v)m_2[/math]. Or [math]m_1 = \frac{u_1+v}{u_1-v}m_2[/math].

>>10194755
If you interpret the pictures in the mind as neurons, then sure.

>>10194825
>equivalently, there is a subsequence that is not increasing, and hence has an upper bound

Beautiful, many thanks. My only question is why does [math]\lim \text{inf} (x_n) \leq \lim\text{inf}(y_n)[/math] hold

>>10195025
Intuitively, because the sequence [math]y_m[/math] only picks some values of the sequence [math]x_n[/math], so the minimum value of the sequence [math]y_m[/math] at any point is also a possible value of the sequence [math]x_n[/math], so the infimum is possibly lower for [math]x_n[/math].

>>10189237
Ok, here's the answer. I'm 85% sure about the stereochemistry in the first step of the second one.
What's the kind of "special instruction" that they want? Temperature? Addition order? Nitrogen atmosphere?

Also this stuff is pretty easy, you should be able to find direct examples on a ochem book!

How do I solve these . The first one was retard easy but I don't know the rest. I thought I would just add the vectors and use cos law but it didn't work. I'm guessing nw and sw mean 45°.

>>10195210
If you promise not to post tilted 3MB images again I might help you out

>>10195232
4chan makes it sideways. Here's the answers

>>10195232
I think this will work

>>10195232
>>10195304
>>10195307
Ok I guess. Still, your filesizes are 30 times larger than required. What's with this compass heading notation, is that also part of what you call "common core"? Pretty weird.

Doing some differential equation solving by eigenvalues and eigenvectors. It's two masses between two walls, with three springs inbetween.
Now then, when getting to the eigenvalue, I get to
(For short, using w^2=k)
(2k+(λ^2))^2=k^2
Clearly, this is going to land me into the complex numbers. Is doing λ=+-iw enough, or am I going to have to take into account λ=+-sqrt(3)w too?

>>10195473
If you get a solution λ=a±ib, you only need one of those two complex conjugates. So, you could pick +iw and +isqrt(3)w for example.

when an ellipse or circle is viewed in perspective, how do you determine the angle of the major/minor axis of the transformed ellipse?

whats the maths

>>10195516
You mean the angle between minor and major axes, or what? You want to transform into projective space or the other way around? Explain more.

Am I supposed to use the definition of a surface integral here?

>>10194772
False.
Consider say a(n)=n+(-1)^(n).
a(2n)=2n+1>2n=a(2n+1) so a isn’t eventually increasing.

>>10195559
>surface area above the region
I think it is, but that's a weird expression.

America explain?
Shouldn't it be like ln something?

>>10195600
>ln something
Why would the answer be ln when u(t) is some function of e?

>>10195606
Oh, should have given context. Just looking at integrating pt, wouldn't it be like -2ln(2t+50), and then the ln and e's cancel out so -2(2t+50)?

>>10195545
the angle between unchanged major and major in perspective.

It seems like ellipses are always transformed into ellipses at certain angles in perspective so I was curious about the math involved

>>10195616
It's [math]\frac{1}{2} \ln{2t+50}[/math], the 0.5 is where the square root comes from.

>>10195658
Do you know how the .5 becomes square root? Is there a rule or name that I can look up?

>>10195667
>>10195658
Like, I guess using some 20/20 hindsight 0 logic reasoning, it's .5*(ln(2t+50)). Does the e just cancel the ln(2t+50) part and leave the .5 floating in the air?

>>10195516
pass to projective space, apply the linear transformation that you want, then go back to affine space

>>10196021
New
>>10196021
New
>>10196021
New
>>10196021
New

>>10195705
ln(ab) = ln(a)+ln(b), so ln(a^b)=b ln(a)