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/sci/ - Science & Math

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10306622 No.10306622 [Reply] [Original] [archived.moe]

Post your stupid questions ITT or general questions that don't need a long thread to discuss them.

I'll go first,

What is the geometrical shape name of this mailbox/tunnel type of shape?

>> No.10306707

Prolonged hypertension causes your heart to work harder and grow stronger as a result. If some recreational athlete had high blood pressure for years and suddenly took regular ace inhibitors or the suchlike would his cardiovascular performance suddenly increase or would the heart muscle just atrophy very quickly or does it not work like that?

>> No.10306738

The human body is very efficient. It will atrophy anything not being used to the level it needs to be in order to maintain itself at that level.

>> No.10306750

What is the permeability of free space?

>> No.10306761

1.25663706 × 10^-6 m kg s^-2 A^-2

>> No.10306765
File: 59 KB, 1368x1054, tmp.jpg [View same] [iqdb] [saucenao] [google] [report]

Let [math]f[/math] be a function, let [math]x,k \in \mathbb{R}[/math]

Now I search for some way I could implement an algorithm that would tell me the x-position if I started at [math](x,f(x))[/math] and "walked" [math]k[/math] steps along the graph.

In the end I would like to have some function (if this is possible) where I just do [math]g(f,x,k)\rightarrow \mathbb{R}[/math].

Anyone has a clue how to do this?

>> No.10306771
File: 109 KB, 900x650, 1540861668393-min.jpg [View same] [iqdb] [saucenao] [google] [report]

To sum it up:
Set up a function from the reals to the coordinate pairs of the function, e.g. [math]t \rightarrow (t, f(t))[/math], parametrize it by arc length then fiddle around with the parameters until you get what you want.

>> No.10306772

arc length from 0 to x is defined by [math] \int_0^x \sqrt{1+f'(q)^2}dq[/math] so if you set that equal to [math]k[/math] and solve for x you're done

>> No.10306784

sorry, didnt see the "start at x" part
[math] \int _x^h \sqrt{1+f'(q)^2}dq[/math] then set this equal to k and solve for h given some x

>> No.10306788

I had an exam question that said

>for how many values of x in the interval [0;2pi] is 2cos^2(x) a natural number. I gave 8 as an answer but apparently it was 9, though they didn't explain it. Why?

>> No.10306793

thank you a lot!
I already got this far, but I am not really satisfied with the need to fiddle around with the parameters, because I assume this would need a lot of calculations and trying out, but I would like to do this programmatically and as fast as possible.

Ok, I will try that. But I am not sure how I can solve for k programmatically without a bunch of trying out. Thanks anyway

>> No.10306796

It's closed [0, 2pi], so one of them repeats.

>> No.10306798

Is P=NP?

>> No.10306803

because 0=360?

>> No.10306804

Probably not.

>> No.10306808

if i use the american maths resources in the sticky to prepare myself for studying chem at uni, will i have to unlearn stuff seeing as i'm in the uk or is it just the universal principles that are important?

>> No.10306816

>calc exam today
>just figured out yesterday that the entire point of the dirac delta function is that when you integrate it with a test function you get the value of the test function at x=0

Absolutely fucking epic. My question is how should I kill myself, exit bag or chad up and buy a handgun?

>> No.10306828

Calc notation is varied, but it's not nationalized.
Kinda weird that you see the DDD in Calc.

>> No.10306831

I don't really know what the equivalent to my course would be in English, so I just winged it and said calc.

>> No.10306835

"Functional Analysis", "Linear Analysis", "Distributions", "PDEs", etc.
Usually distributions show up in one of those.

>> No.10306861

It was some kind of math for physics student class, right? second year?

>> No.10306869


>> No.10307419

if earth had a ring system, would that screw anything up for us? like, are there radiation or climate effects that would be so large as to significantly alter our lives? or would the most practical effects just be on the appearance of the sky and the places you're able to put a satellite?

>> No.10307434

Not so much. It would shade the planet to a certain degree, but since it has already settled into a ring shape, there shouldn't be any debris problems. If a space elevator or other such structures were actually possible for Earth then it'd be in the way.

>> No.10307456

What is the point of calculus in terms as layman as possible?

>> No.10307485

it makes things easy

>> No.10307486

Ah shit. A little less layman plz. As if you were explaining to a high school student just about to start calculus.

>> No.10307494

Calculate the speed at which things happen and how much of a thing has happened once you know the speed.
Also optimization techniques and measuring areas, volumes, and n-dimensional equivalents.

>> No.10307502

it deals with change
and change can be used for tons of stuff like >>10307494
optimization is the largest/lowest point on your function
which happens when the function stops changing

and describing physical situations in terms of calculus and how objects change makes them way easier to write down and solve,

>> No.10307547

It's the basic algebra babby-tier version of analysis, but you can't solve most math problems without it.

>> No.10307552

It's one more tool you have to know how to use before you're capable of touching real math.

>> No.10307601

How do you obtain all the complex roots of [math]x^4+1=0[/math] ? By taking the 4th root of the equation I get [math]\pm i[/math], but those aren't all the roots. I know I'm doing something wrong please help.

>> No.10307610

Use de Moivre's.

>> No.10307612

look up the roots of unity

>> No.10307622

Thanks. I love you.

>> No.10307729
File: 191 KB, 1174x1626, 34e4877b0c661479ef5f7bf8d4fadbb9.jpg [View same] [iqdb] [saucenao] [google] [report]

Calculus was born from attempts at solving two different and (seemingly) unrelated problems: first, the problem of calculating the areas and volumes of non-rectilinear figures (for example, a circle or a sphere); secondly, the problem of finding the tangent to any given curve. The first problem (finding areas) led to Integral Calculus, while the second (finding tangents) led to Differential Calculus.

Integral Calculus can be said to be older than Differential Calculus since it can be traced back to Archimedes' works which used the so-called "method of exhaustion", which was basically a very primitive method of calculating limits of sequences. The method of exhaustion itself is probably even older than Archimedes, since it is found in Euclid and was probably discovered by Eudoxus even earlier.

Differential Calculus is much younger since before the invention of Analytic Geometry the problem of finding tangents to curves wasn't really felt that much. Fermat and Descartes developed some rudimentary methods to find tangemts at certain classes of curves but it was with Leibniz and Newton that the ideas of using "infinitesimals" took root, and that idea was later developed into the modern concept of limits (chiefly by Cauchy). There exists also non-standard Analysis which rejects Cauchy's concept of limit in favor of the older idea of infinitesimals.

Even though Integral and Differential Calculus originated in order to solve two very specific geometric problems, it was soon realized that the methods of Calculus had much wider application. Integral Calculus can be used to describe how a certain variable quantity (which varies over time, or with respect to another independent variable) accumulates as the independent variable increases.

(to be continued)

>> No.10307767
File: 158 KB, 850x604, __flandre_scarlet_and_remilia_scarlet_touhou_drawn_by_beni_kurage__sample-c53702ec82623a4098ca33ae4b8fe53b.jpg [View same] [iqdb] [saucenao] [google] [report]


>> No.10307812

You're trying to make 268375 chairs for a chair convention. This seems like a rather daunting task, but your good buddy Jimmy (who is rather shady, and you don't remember how you met) gives you a button that will pop chairs into existence.
The only problem is, it doesn't give you a solid amount of chairs each time, only giving you 10-20. To make things worse, it only pops up once every 2 minutes.
What is the average amount of time it will take (in hours) to have enough chairs for the chair convention, and what will you do with the chairs afterwards?

>> No.10307818
File: 10 KB, 261x220, 14cf947644975c3b1207eb4ab0d59595895136b9b8aea1d6da645738e8a56aa0.jpg [View same] [iqdb] [saucenao] [google] [report]

To see this, consider a function whose graph lies wholly in the first quadrant (this is the easiest case to understand): suppose that the function f is defined on some interval [a, b], where a and b are both positive. If we think of [a, b] as an interval of time, we are starting at the time x = a. As x increases, the value of the function f will generally change; for a very small interval like [x(0), x(1)] where x(0) and x(1) are relatively close to each other, you can calculate the area accumulated under the graph of the function f by approximating it with f(c[1])*(x[1] - x[0]) where c(1) is any number in the interval [x(0), x(1)]. By dividing the interval [a, b] in many small subintervals, [x(i - 1), x(i)], and summing together terms of the form f(c)*(x - x[i - 1]), you get a Riemann sum which approximates the area under the function, and by taking the limit you get the exact value of that approximation, which is the Riemann integral of the function.

Now suppose that our function f represents some definite concrete quantity, like the velocity of a particle on a straight line. Let's suppose that this particle can move left and right on this straight line. Let's call the particle P and the line r. Our function f represents the velocity of the particle P, and when P moves to the right on line r the function increases, and when P moves to the left the function decreases (in other words we assume that the positive direction on line r is towards the right).

As particle P moves during the time [a, b] we know that the value of f at any given time c represents the velocity of P on line r. So at any time c, f(c) tells us how fast P is moving and in which direction (left or right. Though in our example P is always moving to the right at different velocities, as we suppose f to lie always in the first quadrant). What about the area under f over the interval [a, c]? What does this quantity represent?

(to be continued)

>> No.10307824
File: 698 KB, 3000x3000, 449fa358-a3a3-4cc1-8029-6a4b3e2424e0_1.974e2424c20abbeb9f59e8fd2abc1425.jpg [View same] [iqdb] [saucenao] [google] [report]

Hello, i have never used a ti - 8* calculator, is a ti-89 appropriate for elementary statistics ?


>> No.10307857
File: 991 KB, 3904x3508, __flandre_scarlet_and_remilia_scarlet_touhou_drawn_by_shan__f4221eb2856873ad0e917bc3d1cf77f3.jpg [View same] [iqdb] [saucenao] [google] [report]

Calculate the minimum and maximum possible times. The average should also be the median, but there might be rounding errors.

>> No.10307864

i was hoping for a quick answer, so while I waited, I got someone else to do it for me.

>> No.10307870

Why can't I build muscle?

>> No.10307877
File: 1.02 MB, 1960x1568, ea8658c09ddacbb94bd5170f26ad4f6e.jpg [View same] [iqdb] [saucenao] [google] [report]

If you try to approximate it with a Riemann sum, you get for each subinterval a product of the form f(c)*(x - x[i - 1]) and you sum all the subintervals to get the Riemann sum. (Remember that c(i) is a random point in the interval [x(i - 1), x(i)].) Each term is a product where a random value of the function f in the interval [x(i - 1), x(i)] (the value f(c)) is multiplied by the length of interval (namely, (x - x[i - 1])). In other words, each term of the Riemann sum is a rectangle with base (x - x[i - 1]) and height f(c). If the interval [x(i - 1), x(i)] is reasonably small, then the value of f will not vary that much during this time interval, and therefore the area under the graph of f can be approximated by taking a random value f(c) in that interval and multiplying it by the length of the interval itself. Summing up all these small rectangles you get the Riemann sum. What does each rectangle represent? If f is the velocity of particle P and the interval [x(i - 1), x(i)] represents a small time interval, then the product f(c)*(x - x[i - 1]) (which is the area of the rectangle) represents the distance traveled by particle P while ASSUMING that during that time interval P had a CONSTANT velocity equal to f(c). When you sum all these products, you get a Riemann sum which approximates the distance traveled by the particle over the whole time period [a, b]. You divide the interval [a, b] in many small subintervals so that you can approximate the velocity of the particle during each one of those subintervals with a constant velocity, instead of a variable one. The smaller the intervals, the better the approximation; and as you take the limit of the Riemann sum, you get the exact value of the integral, which tells you exactly how much distance the particle P traveled during the time interval [a, b].

(to be continued)

>> No.10307879

if [math]p^{2} - q^{2} > r^{2} - s^{2}[/math] then is [math]p - q > r -s[/math]? Assuming that [math]p, q, r, s >= 0[/math]

>> No.10307883

Ask your professor what is allowed in the course. Would be a shame to get something and not be allowed to use it. If you're just asking what could help you along the way if no restrictions, then TI-83 and higher work well.

>> No.10307888
File: 1.77 MB, 1341x1300, __flandre_scarlet_and_remilia_scarlet_touhou_drawn_by_ramudia_lamyun__21648c9b962de2d98b6e2b9de9e9f830.jpg [View same] [iqdb] [saucenao] [google] [report]

No problem, I really just wanted an excuse to post Flan.
Think of it like this:
Does [math]p^2+s^2>r^2+q^2[/math] imply [math]p+s>q+r[/math]?

>> No.10307892

I ended up getting a ti-89 titanium for free, so i'm seeing if i really need to buy a 84/83 like the course requires. syllabus says i can use whatever calc i want but that 84-83 is what the course is based on and compatibility is up to me

>> No.10307906
File: 2.12 MB, 1632x1927, fe3367b307f458bddd9c70165bfc231b.jpg [View same] [iqdb] [saucenao] [google] [report]

I forgot to mention that f(c)*(x - x[i - 1]) represents the distance traveled during the interval [x(i - 1), x(i)] because f(c) represents a velocity while (x - x[i - 1]) represents time, so of course their product is the distance.

So Integral Calculus tells you how a quantity accumulates over time when you have a function which describes the rate of change of that quantity over time. Conversely, if you have a function which describes how a quantity accumulates over time, you can use Differential Calculus to find the rate of change of that quantity over time (this is actually easier to understand than integration so I won't bother with a detailed explanation).

So integration and differentiation are inverse operators on functions and they allow you to understand the behaviour of functions and that can be useful in a variety of fields from physics to economics.

>> No.10308006

If we have two alphabets, A1 and A2 such that
A1 = {if, then}
A2 = {i, f, t, h, e, n}

Is A1∗ ∩ A2∗ = empty?

>> No.10308032

rectangularly-extended semicircular prism

>> No.10308051

there are only 3 possible solutions, f(x) 2cos^2(x)=0,1,2. In [0,2pi]:

f is 0 when cos is 0, in pi/2, 3pi/2
f is 1 when cos is plus or minus 1/sqrt2, in pi/4, 3pi/4, 5pi/4, 7pi/4
f is 2 when cos is plus or minus 1, in 0, pi, 2pi

in total that's 9 solutions

>> No.10308064

>no sleep
>no protein
>no exercise
>no actual effort in your exercise (if you're doing 20 curl sets with minimal weight or bodyweight squats, this is you)
>not enough calories for life
If you're a lardass, it's probably the "no actual effort in your exercise" one.

>> No.10308086


1=10-9\not> 5-3=2[/eqn]

>> No.10308273

I need a very fast (O(1) kinda fast) way to check if a given element is in a set A of N elements, where all the elements of this set are generated by a polynomial function. Like, A = {k_1, k_2, k_3, ..., k_N | k_i = P(i), where P is a polynomial}

I know this one procedure that achieves this for sets with elements of the form b^x | x ∈ ℕ and b is a constant. For instance:

if A = {30,31,32,33}, then n = 36
you can see that:

n mod 3^i = 0 | 0<=i<=3 and i ∈ ℕ
Is there a similar procedure for achieving the same thing for sets "generated" by polynomials?

>> No.10308430

Seems good enough, thanks.

>> No.10308695
File: 454 KB, 668x445, pretty solid tbh.png [View same] [iqdb] [saucenao] [google] [report]

Current physics undergrad whose interests are mostly in theory, is it true I'll make literally no money if I pursue this? Its what I find the most interesting but have been considering switching to applied physics so I can pay off my loans before I die, as the majority applied physicists make a good amount more than your average theoretician. What do /sci/? Passion or money?

>> No.10308798
File: 107 KB, 800x356, 800px-Hiragana-Katakana-Romanization.jpg [View same] [iqdb] [saucenao] [google] [report]

Memorization tips?
I've trying to memorize some hiragana and katakana.
Basically all I've been doing is writing 5 characters repeatedly and their sounds, but I feel this is too slow.

>> No.10308826

why don't the authorities crack down on money laundering that goes on at auction houses? i'm not just talking about multi-million dollar fine art, i'm talking about the everyday small items that go for much higher prices than they should. don't be naive, prices are far more rational on websites with a digital money trace like ebay. at old school auctions criminals can bid anonymously, pay in cash, and then sell the items as personal property without even having to pay taxes.

>> No.10308834
File: 397 KB, 1280x1417, shapes.png [View same] [iqdb] [saucenao] [google] [report]

>doesn't know what a mailboxogon is
srsly why even post

>> No.10309023

Write English using the characters you already know. As you gets more proficient with these characters replace more English syllables. Try to write English entirely in Japanese characters.

>> No.10309086

Don't tell me you've paid for university with your own money? Isn't common that this will not end good?

>> No.10309204

What would be a reliable method in Python to find the root of a complicated function such as this one:

[math]f(x) = n - \sum_{k_x} \sum_{k_y} \frac{1}{\exp( E(k_x, k_y) - x) + 1}[/math].

Where [eqn]n[/eqn] and [eqn]E(k_x, k_y)[/eqn] are known. I've tried a few with no success.

>> No.10309211

Undergrad is meaningless anyways. Do want you want to do. The real question is IF you do a PhD, and on what then.

>> No.10309220

Are you the same guy that asked about sums of the form [math]\sum a_i\prod b_i[/math]?

If so, you shouldn't need to be told that you can't ask a question as general as this. In fact, carefully choosing n and E, you can recover the Riemann hypothesis yet again...

>> No.10309230
File: 195 KB, 1042x974, Pyrrole.jpg [View same] [iqdb] [saucenao] [google] [report]

I'd like to know why the intermediate of pyrrole acting as a nucleophile at the 2-position is lower in energy than the intermediate of reaction at the 3-position.
The only explanation I've seen is that the 2-position intermediate isn't cross-conjugated, but I thought cross-conjugation was a different phenomenon to what is seen in the less stable intermediate.
E is a non-specific electrophile in the picture.

>> No.10309233

No, I'm not that guy. I just want to know what's a good Python routine to find the roots of complicated, single-variable, scalar functions. In my case, [math]E(k_x, k_y)[/math] is a well defined function in my code for which I know the value for every [math]k_x, k_y[/math]. To clarify matters further, [math]E(k_x, k_y)[/math] is the electronic band structure of a material, the summand is the Fermi-Dirac distribution and [math]x[/math] is merely the Fermi level. Therefore, I'm actually calculating the Fermi level. I've tried some routines, like scipy.optimize.newton (that requires an initial guess) and scipy.optimize.fsolve, but none have converged.

>> No.10309246

The problem with this is that for whatever reason you assume or expect me to understand (implicitly) how E behaves, or how many values of k_x and k_y there are. Are we talking about an infinite double sum? Are we talking about a decaying function?

Mathematicians spend their lives trying to understand sums that are less complicated, like [math]\sum_{n=1}^\infty \frac1{n^3}[/math], and you expect us to understand an entire family of functions that could well have no convergence...

>> No.10309253
File: 13 KB, 236x236, paraboloid.jpg [View same] [iqdb] [saucenao] [google] [report]

[math]E(k_x, k_y)[/math] is approximately a paraboloid, like pic related. The double sum is not inifinite.

>> No.10309257

ok this one is probably the stupidest one on here by a long shot but;

there are 1 of each of these 7 boxes, red, orange, yellow, green, blue, purple, pink.

you will get three at random. what are your chances of getting green?
(I know if you were just getting 1 it would be 1/7, but after each box you get, the chances go up, 1/7, 1/6, and then for the third box 1/5)

follow up question; what are your chances of getting green in the 3, but not red?
(also if you could explain how you got it that would be really appreciated, sorry this question sucks)

>> No.10309274

>you will get three at random. what are your chances of getting green?
>(I know if you were just getting 1 it would be 1/7, but after each box you get, the chances go up, 1/7, 1/6, and then for the third box 1/5)

Probability it is the first box or it is not the first box and is the second or is not the first or second box and is the third. Which is:
1/7 + 6/7*1/6 + 6/7*5/6*1/5 = 3/7

>follow up question; what are your chances of getting green in the 3, but not red?
>(also if you could explain how you got it that would be really appreciated, sorry this question sucks)
Probability first box is green and not red or probability first box is not green and...

>> No.10309276

Thank you! and the order of them doesn't matter I forgot to write that part.

>> No.10309294

probability that 1 of the 3 boxes will be green but none will be red

>> No.10309364

If the sum is not infinite then you're probably just fucking up the input, or you should improve your initial guess.

>> No.10309386
File: 300 KB, 800x600, __flandre_scarlet_and_remilia_scarlet_touhou_drawn_by_hemogurobin_a1c__429572a2186783fa005b502ca3dc710e.png [View same] [iqdb] [saucenao] [google] [report]

Ezra Pound once mentioned he knew a guy who could read Chinese by recognizing the pictographic characters. IIRC japanese is close enough, try to associate what the letter looks like.

>> No.10309475
File: 128 KB, 750x404, hardly-essayists.jpg [View same] [iqdb] [saucenao] [google] [report]

Find the sum of the following series after 500 terms:
I can tell that the difference between terms is the series 1,2,4,5,7,8,10,11,13 which is the natural numbers minus multiples of 3, but how do I fucking sum that?

>> No.10309500

Group them into pairs.

>> No.10310160

Is the following an NP problem?

You have x number of boxes, of size X, Y, Z (different for each box). How big of a box is necessary to pack all of them into it?

>> No.10310173

How long would it take to learn algebra, geometry, and pre-calculus? I want to go back to school in the fall and will need to take calculus. I'm taking in work hours. Not some broad range. In public school it would some how take 3-4 years if u had no agency.

>> No.10310220

I lol'd too hard at this. Thanks.

>> No.10310239
File: 18 KB, 363x241, diagonalecantor.jpg [View same] [iqdb] [saucenao] [google] [report]

Could someone explain this to me in an easy way? I'm a dumbfuck (cantor's argument)

>> No.10310256

Suppose the reals could be put into a bijection with the natural numbers.
Then we could write them in a list, like the one in the picture.
So we take a diagonal slash across the listing, that is, a number that has at least one digit different from each one in the list. This one is never listed, because the diagonal slash has a different digit from every number listed, which means it doesn't show up in the enumeration. Since we can do a diagonal slash to any possible enumeration, there is no enumeration which doesn't skip at least one number, and thus there are no bijections.

>> No.10310257
File: 486 KB, 2160x555, 20190119_162600.jpg [View same] [iqdb] [saucenao] [google] [report]

Can someone help me with this thank you.

>> No.10310270

The first thing you have to understand is how decimals work. A real number that is not rational has an infinite decimal expansion. As such, you can enumerate the "position" at which you have a decimal number. For example, the number 0.01359... has a "3" in position 3 and a "5" in position 4. This means there is a bijection between the naturals and the decimal position, as described in the previous example.

Now here's the proof: Assume you have an explicit bijection with the naturals to the reals. Then you can list the real numbers in a list starting by the real that corresponds to 1, then to 2, etc.
Now create a number such that at position 1 of its decimal expansion it has a value of 1 more than the position 1 of the real corresponding to 1. Then do the same with 2, 3, etc...

Since the decimal expansion is also in bijection with the naturals, and you have exhausted all the naturals in the previous process, creating a real number different from all in the list, then you get a contradiction.

>> No.10310276

You have an infinite list of reals between 0 (inclusive) and 1 (not inclusive), in some arbitrary order. Construct another such real by taking the diagonal digits (the first digit after the decimal place of the first number, the second digit of the second, and so on) and changing it (e.g. adding 1 modulo 10, so 9->0).

The resulting number isn't equal to any of the numbers in the list. It isn't the first number (its first digit differs), it isn't the second number (its second digit differs), and so on.

IOW, you cannot enumerate the reals between 0 and 1. Whatever infinite list you come up with will be incomplete. By extension, the complete set of reals cannot be enumerated either.

>> No.10310283

Draw a parallelogram, with the vertices labelled in this order : OABC, that is, C is connected to O. Then draw the point defined by the diagonals, that is, the middle point F of the parallelogram.

Notice that OB = a+c, since you travel to it by going to OA then AC, and AC is parallel to OC. Clearly F is in the middle of the path OB, so OF = 1/2 (a+c).

Similarly E is in the middle of FB, so EB is 1/4 (a+c). Now going back to A from B is 1/4 (a+c) - c .

>> No.10310285

just look at the resonance

>> No.10310293
File: 18 KB, 1194x736, diagram.png [View same] [iqdb] [saucenao] [google] [report]

i was drawing this before you posted this, so here's the picture

>> No.10310343

I think that I got it now. Thanks a lot guys

>> No.10310459
File: 5 KB, 510x326, summ.png [View same] [iqdb] [saucenao] [google] [report]

How can I isolate a or b or at least make one of them equal to a single summation?
How do I eliminate summations in summations?

>> No.10310758

The inner term is just (a+b)^k.

You can put k=i+j and rewrite the summation as
[math]\sum_{j=0}^n \sum_{i=0}^{n-j} {a^i b^j (i+j)! \over i! j!}[/math]
Then you can move the b^j outside of the inner summation.

>> No.10310870

But you still have 2 summations

>> No.10310882

wait until analysis 2

>> No.10310892

this is the binomial coefficient, but in general there isnt a way (i dont know of one) to reduce the number of summations

>> No.10310894

have you tried a hash table?

>> No.10311092

So the answers for e to f is the same as f to b? I see how 1/4(a +c) would land on the mid point. I don't understand how you would make e to a. 1/4 (a+c) + 3/4c?

>> No.10311156


back to school kid

dont fucking @ me again

what this (reddit) space

>> No.10311193


>> No.10311277

Do I need to have publications from my master's program in order to get admitted into a phd program?

>> No.10311305
File: 1.19 MB, 3264x1836, 20190119_200650_001.jpg [View same] [iqdb] [saucenao] [google] [report]

Trying to learn calculus atm and ran into a mental block. Assuming y = pi/4, why can't I algebraically solve this to get sin(x) = sqrt2/2? I know it is, that's clear, but what the fuck am I doing wrong? Pic related

>> No.10311334

So for a given polynomial P with integer coefficients, a range of integers [a, b), and an integer n, you want to determine whether n = P(m) for some m in [a, b)?

Do you need to do a lot of checks for the same (P, [a, b) ) pair? Can you precompute a search structure for it?

>> No.10311337

You niggas ask the most absolutely surreal stuff.
Anyhow, we have [math] sin(x)+ \frac{ \sqrt{2}}{2} = \sqrt{2} [/math].
So we subtract [math] \frac{ \sqrt{2}}{2}[/math] from both sides to get [math]sin (x)= - \frac{ \sqrt{2}}{2} [/math].

>> No.10311342

>2 sin(x) + sqrt(2) = 2 sqrt(2)
>2 / sqrt(2) sin(x) = 2
What happened in between those steps?

>> No.10311505

Ayy lmao and I crossed that path out too , some reason it didn't click in my head. It's been a long week

I divided by the sqrt

>> No.10311588

tfw boomer and zoomers on this site are smarter and more knowledgeable than you

>> No.10311730

>I divided by the sqrt
u forgot +1

>> No.10311784

I dropped school when I was 16. The last thing that I remember are polynomials and the basics of linear equations. Where should I restart now? Any good book (that I can find on libgen?)

>> No.10311814

If I have an object (mass m) at position p1, what is the force I need for an impulse to move it from p1 to p2 in t time considering gravity?
I'm sure there is a formula for this, I just can't find it...

>> No.10311911
File: 2.40 MB, 800x5544, A Guide.png [View same] [iqdb] [saucenao] [google] [report]

Khan academy is the laziest and free approach. takes more time but less effort. Otherwise, Lang's Basic mathematics or Gelfand's books do the job

>> No.10311947

Khan Academy -> A Transition to Advanced Mathematics

>> No.10311952

from another thread:
>If you understand DNA you cannot believe in race.
can i get the eli5 version of why?

>> No.10312040
File: 88 KB, 745x511, The+gap+between+us+and+them+could+be+interpreted+in_2f8383_5736938.jpg [View same] [iqdb] [saucenao] [google] [report]

it's SJW bias, just that you can't prove strawmans like "this gene is responsible for why black people love watermelon", there are still 'population groups' in research involving DNA, and there are obvious differences between e.g. aboriginal australians and the inuit people

>> No.10312451

Is there a need for mathematical rigor in physics?
It seems that physicists are often criticized for overuse of approximation or a lack of rigorous methods.
I personally have an easier time understanding mathematical abstraction than physical phenomena, but I still aim to study physics. Am I setting myself up for disappointment?

>> No.10312529
File: 38 KB, 444x542, Rxn Scheme - Mystery Lab.png [View same] [iqdb] [saucenao] [google] [report]

Does anyone know which reactions are involved in this mechanism?

I'm pretty sure the first three steps are an aldol condensation, i think the fourth/fifth is an aldol addition. Not sure about the last step.

>> No.10312558

why would you post this in /mg/ and then in here?
you do realize physicists aren't welcome here on /sci/ right?
this board is for math and science. not for crackpottery.

>> No.10312671

Sometimes I will type out a stupid question here and then I'll realize my mistake before posting. Aye, knowing you guys are here gives me safety.

>> No.10312677

So I have a question about joint probability distributions, such as:

[math] f(x) = \left\{
24xy & \quad 0\leq x \leq 1, 0 \leq y \leq 1, 0 \leq x+y \leq 1 \\
0 & \quad otherwise
\right. [/math]

\int_{0}^{1}\int_{0}^{1-y}24xydxdy [/math]

Like I understand how to solve the problem, like you can subtract either the x or the y and move it over to the upper bound or whatever depending on how you want to integrate it, but I'm having trouble actually visualizing what's going on if you were to look at a graph of it. Could anyone post a picture breaking it down step by step from a graphical perspective or just explaining it?

plz no bully

>> No.10312705

how do I find average velocity if v(f) and v(i) are both 0

>> No.10312720

What are f and i? If all your observations read zero velocity, the average is: zero velocity.

>> No.10312733

initial and final velocity, for the formula average velocity = (initial veloctiy + final velocity)/2

I must be a turbo brainlet because now I'm trying to find it by integrating the function

>> No.10312782
File: 85 KB, 463x444, saddle.png [View same] [iqdb] [saucenao] [google] [report]

> Like I understand how to solve the problem, [...] but I'm having trouble actually visualizing what's going on [...].

I don't understand what exactly you're asking for. If the question is: "how do I get from the definition of f to the integral expression?", here's a picture and an attempt at an answer.

The function 24xy looks like a saddle, the blue lines in the image are equal values of this function. since x and y range in [0,1], and their sum is 1, you can see that the limits for the integration are either "x from 0 to 1, y from 0 to 1-x", or "y from 0 to 1, x from 0 to 1-y". Hope that helps.

>> No.10312789

But what is v(t), do you have a function definition? If yes, what you're doing is correct.

>> No.10312797

sum all observed velocities and divide by number of observations.
If you have a function then its integral divided by projected "length", or [math] f_avg = \frac {1} {b-a} \int_{a}^{b} f(x)dx [/math]

>> No.10312805
File: 19 KB, 1718x152, bbbbbbbb.png [View same] [iqdb] [saucenao] [google] [report]

there is no v(t), that was part of the problem. This was the question.

I still didn't figure it out by the method they wanted from the book.
I wound up just doing the integral (the graph is a basic two-triangles-and-a-rectangle since it's constant acceleration) and found it to be 9.489 m/s

>> No.10312827

Because I want an answer from someone else than a raving lunatic larping as a mathematician.

>> No.10312831

Doing a babby tier proof on fields. I'm trying to prove that the identity element for a field is unique.

So far I have:

Let F be a field. Suppose that p in F has the property that for all q in F we have p*q = q.


p*q = q = 1*q
p*q = 1*q

Now suppose q =/= 0.
By the fact that ab=ac implies b=c if a =/= 0, then p=1.

My problem is, how do I deal with the case that q=0? I can't show that p=1 in that case. But the proposition I'm given says to prove for arbitrary q in F.

>> No.10312839

>there is no v(t), that was part of the problem.
you can easily find v(t) from given data. Just remember that there are 3 different functions for v(t), one for accelerating, one for constant speed and one for deccelerating. Or you could do it with basic math. For 88 seconds average speed is 10, for 10 seconds its 5. It's just a weighted average

>> No.10312843

Did you try just assuming it has two identities?

>> No.10312850

You don't need to. You're confusing yourself. You just need to deal with a single nonzero q.
For instance, just let q = 1.
p = p*1 since 1 is an identity, and p*1 = 1 since p is an identity. Thus p = 1. Done.
You don't need to prove anything "for any q." You assume something for any q, and you want to get a result which doesn't even reference q.

>> No.10312852

Thanks for explaining yourself, moron.
We don't want physicists in our departments. Consider a degree in engineering.

>> No.10312908

Imagine being such a sad piece of shit that you spend your time getting irrationally angry at physics on 4chan.

>> No.10313011
File: 44 KB, 383x499, duckscrete math.jpg [View same] [iqdb] [saucenao] [google] [report]

i'm just trying to sanitize our community

>> No.10313075

>physics is not a science because I say so
lmao indeed

>> No.10313100

Let e and f be two identity elements
then e = e*f = f

>> No.10313179

what makes modern physics a science?

>> No.10313182

what makes modern math not an art?

>> No.10313185

so you're just a faggot who thinks physics=string theory

no wonder you could only get in to wikipedia university for math.

>> No.10313220

So you're not even aware of what science is? Here, first result on google
>Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe
Seems like this definition is an apt description of what physics aims to do. Stop pretending, you obviously don't know shit about anything.

>> No.10313238

it is an art, math isn't a science. but this is the "math and science" board, not the "math, physics, and science" board.

>> No.10313244

modern physics may aim to do that, but it most certainly does not
you mean to say that QFT and modern astrophysics are studied "scientifically?"

>> No.10313249

i'll be sure to read your many papers :^)
you are indeed right this is the science and insecure math board

>> No.10313267

>it most certainly does not
Again, based on the words of an anonymous faggot on an anime imageboard, which I'm not inclined to take too seriously, especially given how you sound like a fucking lunatic

>> No.10313287

>you mean to say that QFT and modern astrophysics are studied "scientifically?"
yes. Not to mention condensed matter physics, bio physics, chemical physics, thermodynamics, optics, the list goes on.

>> No.10313294

Codemonkey here,
I have a question about matrices

I am taking a deep learning class where I see Wx all over the place, where W and x are both matrices. Is it a standard assumption that this is the dot product? That is Wx <=> x . W ?

>> No.10313298

i dont need to convince a physishit of anything, i just need to do my best to make your time on our board hell
feel free to keep posting
ah, so a bunch of other fields then
physics is a joke, glorified engineering

>> No.10313308

ah, so physics is string theory then?

math is a joke, glorified philosophy

>> No.10313322

physics is string theory in spirit
math is not science, it is art. i do not claim that it is anything but philosophy. at least those pursuits are respectable unlike engineering.
you really are seething over this, aren't you?

>> No.10313333



No other major provides a back up plan and I truly enjoy BME.

>> No.10313340

>he's actually proud about spending his free time sperging out about physics on 4chan
How is it that this board has more schizos than /x/? Take your meds

>> No.10313401
File: 1.76 MB, 320x240, mjl2.gif [View same] [iqdb] [saucenao] [google] [report]

>physics is string theory in spirit
so is respectable codeword for "useless" now? I think I'm finally understanding the jargon these mathematicians use. You've been "seething" for about a week now on any thread that mentions physics. Do you do anything else with your life? Pathetic.

>> No.10313559

While i know nothing of deep learning, I somehow doubt that's the dot product, unless you're somehow considering the matrices as vectors over R^(n^2). It's most likely just simple matrix multiplication no?

>> No.10313569

Make a kNN implementation for me in Python 3, shouldn't be many lines.

>> No.10313590
File: 33 KB, 734x198, Screenshot_2019-01-20_19-14-34.png [View same] [iqdb] [saucenao] [google] [report]

what in the fuck am I doing wrong? Says each answer is incorrect.

>> No.10313609

average velocity is change in height over change in time
so the first one if (y(2) - y(2 + .5))/ (2 - ( 2 + .5))
= (y(2) - y(2.5))/(-.5)
which is -32

>> No.10313622

Nope, matricial product.
Remember how you multiply matrices? Pretend the vector is a collumn vector, and multiply Wx.

>> No.10313632

I don't understand, don't you have to divide by ending time minus starting time?

>> No.10313642

whops, sorry disregard that

>> No.10313705

classes haven't started yet, what else am i supposed to do?

>> No.10313718

Ok, so the dimensions of the matrices I am given are
| W | = 16 x 10
| x | = 10000 x 16
and Wx must be
| W x | = 10000 x 10
Obviously the dimensions don't make any sense for a multiplication, but it works for a dot product.

I guess W x_i makes sense for some row i,
is x . W a shortcut for applying multiplication to each row?

>> No.10313721

err W^t x_i that is

>> No.10313732

Dude, if anything it makes perfect sense for matrix product and none at all for dot product.

An n x m matrix has n rows and m columns. To multiply a matrix with another you take the first row of the first and multiply each entry with the entry corresponding to the first column. Then on and on.

>> No.10313765
File: 14 KB, 668x120, Q4.png [View same] [iqdb] [saucenao] [google] [report]

My dumb ass needs help with pic related, if somebody could point me in the right direction... so far I've got:

>g(x) is continuous, therefore integrable, therefore the RHS integral exists
>product of continuous functions is continuous, therefore the LHS integral exists
>in the special case where g(x)=0, both the LHS and RHS equal zero, so any value of c will do
>otherwise we can divide by the RHS integral to get some value k
>if k is within the range of f(x), the existence of c is implied by the Intermediate Value Theorem
>I have no idea how to show this

>> No.10313774

Well I'm a complete fucking retard. Thanks anon, makes a good bit of sense now.

>> No.10313785

It's literally a meme version of the mean value theorem.

>> No.10313834

I figured out my problem.
While written Wx in texts, the operation is actually implemented as xW for efficiency reasons.

>> No.10313836

Notice that f is continuous on a compact interval [a,b], therefore it achieves its extrema. That is, there exists constants L and M such that [math]f(L)\leq f(x)\leq f(M)[/math] for all x in the domain [a,b].

Since [math]g\geq 0[/math], we have that [math]\int_a^b g\geq 0[/math]. Therefore we have that [math]f(L)\int_a^b g=\int_a^b f(L)g\leq \int_a^b fg\leq \int_a^b f(M)g=f(M)\int_a^b g[/math], since [math]f(L), f(M)[/math] are constants.

Hence, the function [math]H(t)=f(t)\int_a^b g[/math] with [math]t\in[a,b][/math] has a maximum at [math]M[/math] and a minimum at [math]L[/math], taking every value in between. So by the intermediate value theorem, you can conclude that there is some [math]c\in[a,b][/math] such that [math]H(c)=\int_a^bfg[/math], giving your result.

>> No.10313858

Is there a non discrete topology where all singletons are open?

>> No.10313866

No, because "any union" means "literally any union".

>> No.10313905

I've been sleeping a lot. Not like nodding off during regular daily activities, but just being unwilling to get up.

I slept for around 18 hours today. Nothing crazy I guess, but I was curious why this is. I wasn't THAT tired, but I just didn't wake up.

>> No.10313908
File: 114 KB, 1280x720, maxresdefault.jpg [View same] [iqdb] [saucenao] [google] [report]

>writing personal statement
>minorities encouraged to apply

Should I mention that I'm a first generation American in my personal statement? Not really sure how to include it without seeming like someone who is a victim/wants gibs. Like, yeah I didn't have the same education resources or a family that gave a shit about education, but bad parenting =/= someone who was oppressed.

>> No.10313914

I'll give you a set. How do you write it as the union of arbitrarily many open sets?

>> No.10314124

If we negate the axiom of choice there is a function f : R -> R that is discontinuous at a point x but sequentially continuous at x. Since we negated choice I expect the proof to be constructive and not just proving the existence non-constructively. Where can I find the proof? If not the proof, how about an example?

>> No.10314141

always, always play intersectionality meme with personal statements

>> No.10314143

Since a lunar eclipse is currently happening over Freedomland, a question about the moon popped into my head. Does the moon rise and set in the sky like the sun does?

>> No.10314153

Thanks, any tips on how to word it? Should I include that as my opening line?

"I never thought I would see myself going into a scientific field. Being the first generation in the United States in my family, I did not have the resources, guidance, or encouragement to excel in an educational setting. "

>> No.10314264

for fuck sake... first, you should learn how the academia and the scientific community works.

after that, publish a paper in any serious, indexed and peer-reviewed periodic/journal. since we are talking about physics, it could be, for instance, Physical Review.

only then you can come here to talk about front-end research.

>> No.10314452

i don't really care, and i'm impressed you're dense enough to think i do. i'm not the one defending my fucking pride over a meme.
also, nice spacing

>> No.10314869
File: 33 KB, 500x500, az-large-3118906.jpg [View same] [iqdb] [saucenao] [google] [report]

Question regarding cosmetics (pic unrelated, don't bother).

Girl A heard from her friend Girl B that this "amazing magical anti-aging cream" did wonders for her ass. Claims within a month of using it, cellulite she had on her ass is gone.
Girl A asked me if it sounds legit. She has enough reason to believe Girl B isn't bullshitting.
I don't know shit about cosmetics or chemistry in general, though maybe one of you anons would know. Or at least point in the right direction. I believe Girl B is honest, but I'm willing to bet one of the active ingredients is either harmful or else all girls in the world would be buying this shit.

To save anyone calling me a shill, I'll just paste the product ingredients here:

> Ingredients:
> pink pepperslim
> guarana plant extract
> collagen
> EcoSlim
> guarana
> red grapefruit oil

> full ingredient breakdown

>> No.10314980
File: 361 KB, 473x675, 1531043642113.png [View same] [iqdb] [saucenao] [google] [report]

So I have an oscillator and its movement is defined by the diffeq (E): y'' = -w^2*y with w =/= 0, and F the set of functions that verify (E).

How do I prove that, if a function y belongs to F, the function g = w^2y^2 + y'^2 is constant?

I got given a hint that it had something to do with a null derivative but I don't see it. Any help?

>> No.10314996

To elaborate:
I tried deriving g and I get

g' = 2wy^2 + w^2(2yy') + 2y'y'' which gives g' = 2wy^2
But that's not equal to zero. Yet it should be if g is a constant.

>> No.10315001

w is a constant

>> No.10315002

Yeah but y is a function that isn't null, so g' = 2wy^2 can't be equal to zero. What is it I'm missing exactly? I feel retarded

>> No.10315004

You're deriving it wrong.

>> No.10315005

I'm assuming you got the first term in your expression for g' by differentiating w, but that isn't necessary because w is a constant, and once you get rid of that first term you get g' = 0

>> No.10315007

Oh, alright. I just got the expression wrong. Thanks.

>> No.10315211

I'm writing my master thesis in physics (cosmology) and use quite a bit of GR and so on. Do I cite Einsteins original paper or is that pretentious? Should I just refer to any textbook on the topic instead?

>> No.10315230

I have a curve c(t)=(a(t), b(t)) with t between 0 and 1, and i want to calculate the integral of f(x,y) dx, how do i do it?
I only have the formula for the integral of f(x,y) dx dy, but in the exercise there is only the dx

>> No.10315286

What are a and b?

>> No.10315288

Write x as a function of t and apply substitution.

>> No.10315294

Absolutely nothing wrong with that.

>> No.10315304

Single variable functions

It worked thanks. but is this method always valid? For example if i had a 3D curve and had to calculate the integral over it of f(x,y,z) dx dy, i would get a (dt)^2 inside the integral which doesn't make sense

>> No.10315364

Yeah, except you can't integrate dx dy along a one-dimensional space.
Thumb rule is that the thing you're integrating along has to have as many dimensions as you have d something, and repeats don't count.

>> No.10315645

I have a Casio scientific calculator (fx-83GT plus).
what is the best for battery conservation; to turn it on and off with 2 minute intervals until my work is done, or to keep it on for the entire duration of my work?

>> No.10315698

Is it common for PhD students (in the field of condensed matter theory, more specifically) to do internships and/or spend time in other universities/departments as visiting students?

I'm asking about American universities in general, but I'd also like to know the answer from European anons if possible.

>> No.10315800

Have my final physics exam tomorrow of 3rd year of engineering. Been studying things like Dzhanibekov effect and dynamic bralancing of axis and its pretty cool, much easier to understand than i expected

>> No.10315849

I have a genetics related question. My GF had childhood appendicitis, her father and grandfather before also had childhood appendicitis. Her brother didn't have appendicitis though. I didn't have childhood appendicitis and nobody in my family did either. If I were to have children with my GF, how likely would they be to get childhood appendicitis?

>> No.10315917

my great grandfather had kidney failure before he died, and now i have chronic kidney disease stage one, i have the same question here atleast in a different way im asking if i got it from him.

>> No.10315968

I mean, you can, but any decent GR text will be more helpful as a resource. There's no real need to have to return to the original source. A good graduate students nowadays knows GR much better than Einstein ever did.

>> No.10316300
File: 2.19 MB, 2582x1937, 2019-01-21_17.19.07.jpg [View same] [iqdb] [saucenao] [google] [report]

What am I doing wrong here? I need to use the two substitutions to find the general solution for the y'' eqn. I keep getting stuck with a higher order u(t) and I can't think of anything.

>> No.10316310
File: 76 KB, 288x402, akkothinking.jpg [View same] [iqdb] [saucenao] [google] [report]

Is there a way to find out how much water you would need to submerge an object?

>> No.10316347

submerge it

>> No.10316358

I'm going to be removing rust from a 7ft tall beam of steel so I'm trying to find out if it would even be worth it to buy enough rust remover to submerge it and let it soak.

>> No.10316398

If you want to solve y''-4y=64, first step is to solve the complementary equation y''-4y=0, which gives y(t)=Ae^(2t)+Be^(-2t) for some constants A and B. Then solve the general equation (i.e. take the 64 into account) to get y(t)=Ae^(2t)+Be^(-2t)-16. Now substitute to find A and B.

>> No.10316412

Only answer for irregular shapes is to submerge it and see how much liquid it displaces. Then take the shape's volume away from the volume of your container. Obviously there are workarounds like putting other objects into your container to fill space that would otherwise be occupied by rust remover.

>> No.10316433

Why does my method not work?

>> No.10316468

Please could you reccomend some books on linear algebra, physics and math analysis for first year student? English is not my native language and I want to improve it but I don't have time to read fiction or watch films a lot

>> No.10316988

probably cos you're a brainlet

>> No.10316998

I know that, but really why?

>> No.10317025

Sketch the interval (3,7) on a number line and label the point 4 inside. Then find a value δ>0 such that 0<|x−4|<δ3<x<7.

>> No.10317151

Is <A_n|v|A_m> just equal to v?

>> No.10317153

In what context? That looks more like the matrix elements of [math]v[/math] to me?

>> No.10317156

Jeebus Cripes, think about it. If you're gonna submerge something in a solution, you'll need a container, like a tank or a pool.

>> No.10317189
File: 506 KB, 2048x1684, Screenshot_20190121-231914.png [View same] [iqdb] [saucenao] [google] [report]

I need to find a function that fits this graph. I get as far as (3(x-2)(x+2))/((x+3)(x-4)) before I'm stumped as what to do next.

Where am I going wrong?

>> No.10317201

just use interpolation like the good engie that you are

>> No.10317202

Anyone here did any toying with wormholes ? Hawking is kinda kicking my ass

>> No.10317216
File: 27 KB, 308x396, 9781305965720_p0_v1_s1200x630.jpg [View same] [iqdb] [saucenao] [google] [report]

Where can I find academic books in math like pic related online?
>inb4 poorfag

>> No.10317221

Is this legit GR or popsci? If it's the former then sorry, can't help you there. My tensor calc is rusty.

>> No.10317227

It's legit GR but no calcs needed, I just need to summarise an article for an undergrad class and like a dumbass I chose Hawking's 'Whormoles in spacetime'.
It's all good until I reach the point where he goes on about how there are three possibilities if a closed universe branches in our region at only one point

>> No.10317228

Talentless neet and complete newfag to this board
No special interests so never could decide a career which is why my life slowed down to a crawl
Is electrical engineering a good trade to take a step into fixing my life
Absolutely garbage at math from not studying shit for over half a decade if that means anything

>> No.10317230

libgen ?

>> No.10317242
File: 7 KB, 445x103, Screenshot_2.png [View same] [iqdb] [saucenao] [google] [report]

Pls help am dum dum
I thought the form cos(x^2) couldn't be integrated

>> No.10317263

you sure you wrote that right ?

>> No.10317273

It's a screenshot of what my teacher assigned.
Maybe he's crowd sourcing a solution that he can take credit for.

>> No.10317291

Well then, Mathematica comes up with Fresnel integral so you go have fun with that

>> No.10317299

Maxima says it's equal to zero. It also gives a formula for the indefinite integral in terms of erf(). Which suggests using cos(θ)=(e^iθ+e^-iθ)/2 (erf() is defined in terms of the integral of e^-x^2).

>> No.10317306

Turns out you're supposed to switch and integrate dy first and then dx. You have to recalculate the bounds too. If anyone cares. It does come out to 0.

>> No.10317310


>> No.10317336

What are all the morons responding to you talking about? You switch the order of integration for christs sake.
Oh thank god.

>> No.10317672 [DELETED] 

Why is this?
(x_1 - x_2)^2 = (y_2 - y_1)^2
x_1 - x_2 = y_2 - y_1 = 0
x_1 = x_2, y_1 = y_2
On the first to second step, do they square both sides? And why is it equal to 0? The math book im using asks this question rhetorically, but never answers it, just assuming im smart enough to figure it out.... which im not. Since all the fucking math books are filled with rhetorical questions without answers.

>> No.10317678

Why is this?
1. [math]x_1 + iy_1 = x_2 + iy_2[/math]
2. [math](x_1 - x_2)^2 = -(y_2 - y_1)^2[/math]
3. [math]x_1-x_2 = y_2 - y_1 = 0[/math]
4. [math]x_1 = x_2, y_1 = y_2[/math]
How do they reach the third step? Square both sides, can you do that with a negative number (even if it's squared)? What is the order of operation there? And why is it equal to 0? The math book im using asks this question rhetorically, but never answers it, just assuming im smart enough to figure it out.... which im clearly not.

>> No.10317681

Take the square root of both sides*

>> No.10317689

More oddities which i don't understand:
[math]-5^2 = (-1)*(5*5)[/math]
Why isn't it instead:
[math]-5^2 = (-5)*(-5)[/math]
Is the definition of a negative number [math]-x = -1*x[/math] or do negative numbers "actually" exist? Are negative numbers "actually" always converted by putting -1 in front of them?

>> No.10317707
File: 142 KB, 1184x586, dawidnad.jpg [View same] [iqdb] [saucenao] [google] [report]

I apologize for the spam but i get so frustrated at this sort of shit... Who is lying to me, wolframalpha or wikipedia? Fuck math man... jesus christ... I should've become a politician....

>> No.10317711

There's no contradiction in that image (-5)^2 = (5^2) = 25 is not the same as -(5^2) = -25

>> No.10317715

Why the fuck would a medfag ever want to work in a private hospital? I'd rather deal with shitty patients than shitty coworkers any day.

>> No.10317724

So [math]-5^2[/math] becomes [math]-(5^2)[/math], if nothing else is stated? Why doesn't it become [math](-5)^2[/math] automatically? I mean, if a negative number is like any other number, I don't see why it shouldn't. Wait is it because it's actually saying [math]-1*5^2[/math] and you calculate exponents before multiplication? Thanks for reply btw

>> No.10317753

>you calculate exponents before multiplication?
Yes that's the usual convention. You may find it helpful to think in terms of functions. Define square(x) = x^2 and neg(y) = -y, then -5^2 is shorthand for neg(square(5)) whereas (-5)^2 is square(neg(5)).

>> No.10317756

Do you really need that much math to do programming and Computer Science? If so, what math do I need to learn?

>> No.10317759

I might not be able to do comp sci at university until next year. What can I do to get ahead so by the time I can do it, I'll be more than qualified to succeed?

>> No.10317761

More stupid questions:

Which way is the "most correct" way of subtracting a number?
[math]5 - 3[/math] or [math] 5 + (-3)[/math]. They evaluate to the same thing, but one is dependent on only addition and the "existence" of negative numbers, the other is dependent on subtraction and the existence of only positive numbers. Sort of. They're not the same anyway, so which one is "truly" correct, according to mathmatical axioms and math law, if that even exists.

>> No.10317764

Hmm, that's pretty good, thanks.

>> No.10317783

What does denumerable mean? Is it the same as infinite countable?

>> No.10317940


>> No.10317996

You are given a test of 20 questions.
These 20 question are randomly picked from a selection of 60 questions total.
You know the answer to 57 of those 60 question.
You take the test 9 times.
What is the % chance you do not encounter the 3 questions you do not know the answer of?

>> No.10318008


>> No.10318214

The latter. Typically in this setting (the more general setting of a group or a ring) we are given how to add things and how to invert them. Then minus is defined from those as plus the inverse.

>> No.10318218

Unfortunately there isn't a convention. That depends on your text and your professor.
It can mean either infinite countable or just countable/finite

>> No.10318333

It sounds like you're looking for the field axioms, which the real numbers obey. These are how people usually conceive of arithmetic on the real numbers. One of the axioms is that for any number A, there is a number B such that A+B=0=B+A. That B is labelled as -A. So negative numbers do have an existence of their own. Ultimately subtraction is defined in terms of negative numbers - the expression X-Y is simply shorthand for X+(-Y). Neither is more correct since they literally mean the same thing, but in the spirit of your question X+(-Y) is what is "truly" happening.

-A is not defined as (-1)*A, although they do happen to be the same. This is because of the distributive property: 0 = 0*A = (1+(-1))*A = 1*A + (-1)*A = A + (-1)*A. Since -A is defined to be the number satisfying A + (-A) = 0, we see that -A = (-1)*A.


>> No.10318370

Squares are always non-negative, so in the second equation you have a non-negative number being equal to a non-positive number. The only way this can happen is if the number is zero.
An alternative way to see it is to bring the right hand side over to the left, giving you the equation for a circle of radius zero. The only solution is that each term is separately zero.

>> No.10318487
File: 61 KB, 960x793, rps20190122_195648.jpg [View same] [iqdb] [saucenao] [google] [report]

Really easy but I want to be sure.
The angle B is 90°. Does D measures 90° too? My guess is no, as according to my calculations BE is √150 but using Pythagoras it's √162

>> No.10318502

An interesting result from the formula you're using is that Pythagoras only works if the triangle is rectangle. It's also an easy way of checking.

>> No.10318504

Yes, it is 90 degrees.

>> No.10318507

it can't be 90º, since pythagoras doesnt work.

learn what the contrapositive statement is.
The "direct" pythagoras says: if the triangle is right angled, a^2+b^2=c^2.
The "contrapositive" pythagoras says: if a^2+b^2 does not equal c^2, then the triangle is not right angled

>> No.10318520

BC is sqrt(150) so BE is sqrt(150)+2sqrt(3). Get BE from pythagorian theorem from right triangle and remember (A+B)^2=A^2+2AB+B^2 (for Abelian groups which the real numbers are). I think you forgot the 2AB term in calculating BE from right triangle and the 2sqrt(3) when calculating from the left triangle.

>> No.10318523

Learn how to apply basic algebra before criticizing others.

>> No.10318530

not only are you wrong, you actually unironically and pretentiously said (A+B)^2 = A^2+2AB+B^2 is an identity for abelian groups lmaooooooooooooo

>> No.10318541

Alright well it is 90 degrees and you're the reason why there isn't intelligence on this board

>> No.10318564

Go to /fit/ and read the sticky

>> No.10318596

Don't worry, he's gonna tell you all about how he just can't grow muscle. The world is against him.

>> No.10318690
File: 129 KB, 1280x720, maxresdefault (1).jpg [View same] [iqdb] [saucenao] [google] [report]

>By 2011, he weighed 200 lbs; when he stepped on the 2012 Amateur Olympia stage, he weighed in at 286 lbs and was declared the champion.
git gud

>> No.10318691

What does this mean and what is it used for?

>> No.10318723

so, does the rectum actually have some kinda sense of taste or not?
pretty sure I can taste the hot peppers from yesterday now after taking a shit

>> No.10318796

>The first thing you have to understand is how decimals work.
I'm a literal math brainlet. I'm trying to get a grasp on it. Can you explain decimals in the simplest way you can?

>> No.10318814

Anyone know a site where you can download course books as pdf?

>> No.10318817
File: 84 KB, 1000x750, me (12).jpg [View same] [iqdb] [saucenao] [google] [report]

how do i find out if i have klinefelters? bit worried because ive got wide hips lol. also, i've had maybe a few dozen blood tests in my life (not for the purpose of diagnosing klinefelters) and given a few urine samples. if i had klinefelters, this would have been picked up and i would've been told, right?

pic related isnt me btw

>> No.10318850
File: 34 KB, 739x443, what the fuck.png [View same] [iqdb] [saucenao] [google] [report]

what the actual FUCK is wrong with my calculator?

im using a ti-83 plus and literally this question is AS SIMPLE AS JUST ENTERING THE NUMBERS CORRECTLY into L1 and L2 and looking at the mean.

i know for a FACT I AM PUTTING THEM IN CORRECTLY but its telling me the mean is 36.5 when its SUPPOSED to be 30.55

what the FUCK is going wrong here?

pic related are the values.

>> No.10318952
File: 202 KB, 754x412, magnetic-flelds-during-reversal.gif [View same] [iqdb] [saucenao] [google] [report]

what would be the result from a theoretical magnetic pole reversal?

will solar radiation blast our atmosphere into space and kill us all?

will the crust shift or the earth's axis tilt to compensate?

is it a doomsday scenario?

>> No.10318958


>> No.10319014

Element wise multiply L1 by L2 then divide by the sum of L2.

>> No.10319019

Look it up its happened before

gene test specifically for XXY. Checking your chromosomes is not routine for any of those so it wouldn't show up.

>> No.10319026

post your pics to /fit/

>> No.10319065

old dude thinking of going back to school for math. what are my options

>> No.10319084

you calculated the average of list 1, you didn't account for the frequencies in your calculation. exactly how you fucked up this badly I couldn't tell you without seeing your work.

>> No.10319089

You're all a bunch of retards. It's called loaf bread.

>> No.10319101 [DELETED] 
File: 2.17 MB, 2820x1453, 1520292065028.jpg [View same] [iqdb] [saucenao] [google] [report]

Can I assume that any set in [math] \; \mathscr{A} \; [/math] contains all reals and also does not contain all reals ? Is that what it is literally telling me ? I am tired and just want confirm.

>> No.10319108

No. The set [math] \mathcal{A} [/math] contains literally no set. Since the definition of the intersection along an empty collection of sets is defined as the universe set, and the union is defined empty, you get the result in the picture.

>> No.10319124

Okay I will keep rereading this until it makes sense. I knew it had no sets, I thought the open sentence I proposed was impossible which I thought leads to an empty set.

>> No.10319130

It's just definitional goofery, don't worry too much about it.

>> No.10319131

There are really only two viable options in my opinion
option 1) you go to school
or option 2) you don't go to school

>> No.10319132
File: 92 KB, 604x837, Capture.png [View same] [iqdb] [saucenao] [google] [report]



>> No.10319141
File: 409 KB, 934x855, Capture.png [View same] [iqdb] [saucenao] [google] [report]


okay, this is epic

>> No.10319145

Based and redpilled.
>surely /sci/ is the correct place to ask this

>> No.10319149

i didn't want to open a /g/sqt tab

>> No.10319161

what's the difference between the reuptake and the autoreceptor in an axon's terminal button? is it just that the autoreceptor additionally detects the number of neurotransmitters released?

>> No.10319339
File: 31 KB, 708x526, bbbbbbbbbbb.png [View same] [iqdb] [saucenao] [google] [report]

I'm writing functions based on the compound interest formula in mathematica

on wolfram-alpha I can just type in a (mathematical) function and it'll output a graph for me.
How can I set a variable in mathematica such that I don't supply it, rather, mathematica generates a range of values based on changing that variable?

in other words, how do I make a programming variable behave as a mathematical variable in mathematica, I guess

the variable in question is shares_

>> No.10319364

What does AB mean in an abelian group where the operation is +?

>> No.10319366

>from sklearn.neighbors import NearestNeighbors

>> No.10319467

What does ^2 mean in an Whelan group where the operation is +?

>> No.10319481

Hehe. I brought this up at work so many times. I think you may be on to somthing or you are as dumb as I. It was argued that peppers would be more of a feeling than a taste and proposed that popsicles would be used. Surely, the difference between banana and root beer could be learned.

>> No.10319483

Fine. I just figured I'd I didn't throw that in there someone would come back saying that expression doesn't hold for non-Abelian cases

>> No.10319542

So you meant in commutative rings.
Sorry, just want to clarify what it is that you should have said in order to be right, instead of what you are currently, which is wrong.
I've never heard of an abelian ring.

>> No.10319644
File: 12 KB, 538x84, stat.png [View same] [iqdb] [saucenao] [google] [report]

i'm having a hard time coming up with an example for part b here. How is not equal to 0?

>> No.10319690

I don't know precisely what the conditions are, but my first thought is P(set containing 0) = 1, P(set without 0) = 0. I think that's just the measure generated by the lebesgue-stiltjes premeasure where the function is just the heaviside.

>> No.10319809
File: 622 KB, 2400x1600, Screenshot 2019-01-23 at 12.05.25 AM.png [View same] [iqdb] [saucenao] [google] [report]

Can someone point out what I did wrong? My answer is very different from what's in the solution manual.
The only big difference is that in the solution manual, the force of friction is going in the opposite direction (meaning the 2m block would be sliding upwards).

>> No.10319838

Are you using a windows tablet?

>> No.10319859
File: 80 KB, 897x768, cutaway3a.jpg [View same] [iqdb] [saucenao] [google] [report]

Both pistols and revolvers have rather long spring that goes through their grips. It's the "main spring", and its function is to push the hammer that detonates the cartridge.
I don't know much about physics, so I was wondering why it is like it is.
Is the grip used because the spring needs to be relatively long, and that's the only place where it would fit? Or is it because it needs to be rather vertical (and if so, why?)?
Why must it be long? Does its length help push the hammer harder? Or does it help make it easier to contract when that must be done manually by the shooter?

>> No.10319874

They're moving at a constant speed 2ma/ma, they're not stationary

>> No.10319875

Why do sound waves need a medium to travel through but not radio waves?

>> No.10320187

Can someone give me the newtonian forces breakdown on why a woman's breasts bounce up and down when they jog?

>> No.10320219


im not done learning neither electromagnetism nor waves yet but... electromagnetic waves are simply a certain "type of" time-varying electromagnetic field (which simply can exist in vacuum)... in particular solutions to Maxwells equations in space free of charge.

On the other hand mechanical waves are the motions in a fluid, the medium they need to propagate.

EM waves are a whole nother deal and if you wish to fully appreciate this id say you need to pick up a book on the subject and read it completely. Theres no useful explanation that doesnt require thr whole background

>> No.10320221

sound are defined as being vibrational waves through a physical medium. radiowaves are part of the electromagnetic spectrum and travel through an invisible medium, the electromagnetic field.

>> No.10320224


The physical constant μ0, (pronounced "mu naught" or "mu zero"), commonly called the vacuum permeability, permeability of free space, permeability of vacuum, or magnetic constant, is the magnetic permeability in a classical vacuum. Vacuum permeability is derived from production of a magnetic field by an electric current or by a moving electric charge and in all other formulas for magnetic-field production in a vacuum.

In the SI system which is going into force in 2019, this value needs to be determined experimentally; 4π × 1.000 000 000 82 (20) 10−7 H·m−1 is a recently measured value in the new system. It will be proportional to the dimensionless fine-structure constant with no other dependencies.[1][2][3]

Before this, in the reference medium of classical vacuum, μ0 had an exact defined value:[4][5]

>> No.10320232

It just needs to be long to have the proper energy and still allow easy pull back of the hammer. If cocking the hammer wasn't a problem then the spring could be really beefy and short, but you'd not be able to pull the hammer back without some other mechanical aid. It is like the different between the limb lengths of a long bow and a crossbow. Really stout crossbows with short limbs require a ratcheting system to pull them back.

The spring in a rifle is in a completely different angle, fyi.

>> No.10320236


>> No.10320238

Consider this:

I have a group G with cardinality 20 that is a subgroup of [math] S_{6} [/math] and it has this structure:
- 1 normal subgroup of elements of order 5 (and cardinality 5)
- 5 cyclic subgroup of elements of order 2 and each subgroup has cardinality 4( thus the whole set has cardinality 15,they are disjointed, without the identity)

Now i want to study the orbits of the action of G on the set [math] X = \{ 1,2,3,4,5,6 \} [/math]
and i will use this formula for that (https://groupprops.subwiki.org/wiki/Orbit-counting_theorem, the first form).


if i count the elements that are fixed by the 5 order elements' subgroup i should get 4 (i'm not counting the identity), because they are cycle of 5 numbers and the number that is fixed by them is the one that doesn't appear in the cycle, thus:
[math] 4 * 1 [/math]

Same reasoning applied to the 5 cyclic subgroups of order 2 is should get 4 fixed numbers for each of them, thus:
if i count the elements that are fixed by the 5 order elements' subgroup i should get 4 (i'm not counting the identity), because they are cycle of 5 numbers and the number that is fixed by them is the one that doesn't appear in the cycle, thus:
[math] 15 * 4 [/math]

Now i count the elements fixed by the identity i get the whole set:
[math] 6 [/math]

Summing all of them i get: [math] 4 \, + \, 60 \, + \, 6 \, = \, 70 [/math]
which it is not divisible by 20, which is an absurd (according to the formula above)

Where is my mistake?

>> No.10320244


I'm sorry, my bad i made a chaos with copying and pasting. Here i corrected the post:

Consider this:

I have a group G with cardinality 20 that is a subgroup of S6 and it has this structure:
- 1 normal subgroup of elements of order 5 (and cardinality 5)
- 5 cyclic subgroup of elements of order 2 and each subgroup has cardinality 4( thus the whole set has cardinality 15,they are disjointed, without the identity)

Now i want to study the number of orbits of the action of G on the set X={1,2,3,4,5,6}
and i will use this formula for that (https://groupprops.subwiki.org/wiki/Orbit-counting_theorem, the first form).


if i count the elements that are fixed by the 5 order elements' subgroup i should get 4 (i'm not counting the identity), because they are cycle of 5 numbers and the number that is fixed by them is the one that doesn't appear in the cycle, thus:

Same reasoning applied to the 5 cyclic subgroups of order 2 i should get 4 fixed numbers for each of them, thus:

Now i count the elements fixed by the identity i get the whole set:

Summing all of them i get: 4+60+6=70
which it is not divisible by 20, which is an absurd (according to the formula above)

Where is my mistake?

>> No.10320336


oh I see, that's interesting

>> No.10320385

Thanks a lot.

>> No.10320397

If anyone on this board has experience with the effects of alcohol and maybe medical or neuroscience knowledge, I would be very appreciative if you could help me with this question.

I have consumed 703 mL of 14% alcohol two times a month, very regularly, for about 2 years now. Is this amount of alcohol putting me at risk of brain damage, or has it already caused it?

>> No.10320449


i don't know orbits yet. is a set of orbits somehow analogous to a factor group? that wiki uses S/G the same notation as my text for a factor group. clearly they're not the same thing though since S is just a set and G is a group instead of a group and a normal subgroup, respectively.

>> No.10320472

Question about logarithm or something similar.
For example I know that log(x) at x=1 is equal to 1 and it goes up by 1 for each tenfold of x (x=10 gives 2, x=100 gives 3). So far so good, but looking at the graph the value inbetween are not linear, so:
1) Is there a way to intuitively warp my mind around how it increases?
2) What function do I need if I want these values to be linear?

>> No.10320473

It's a Samsung Chromebook.

>> No.10320480

>log(x) at x=1 is equal to 1

>> No.10320529

You're right, I fucked up the numbers up there, thanks for the correction. My question still stands, though.

>> No.10320643

"Given p = 0.06. Calculate the probability that, in a 32-Bit-Block, the first and the 32nd Bit as well as 2 additional Bits get transmitted incorrectly". I dont know how to solve that, I can calculate the prob. of 4 wrong bits but I dont know how to handle the positioning here.

>> No.10320716
File: 20 KB, 735x174, Screenshot from 2019-01-23 11-41-20.png [View same] [iqdb] [saucenao] [google] [report]

Can someone help out with this? I'm confused as it's asking for a unit tangent vector at t but there's two t values. and I guess the next part is asking for arc length? This problem just seems overly complicated for no reason.

>> No.10320770
File: 105 KB, 645x729, 1537630166899.png [View same] [iqdb] [saucenao] [google] [report]

Alright, a few in a row:
From "Beyond Perceptualism: Introduction to the Special Issue"
( https://sci-hub .tw/10.1111/1746-8361.12106 )

>(Page 1, 3rd paragraph) According to ‘strong perceptualism’, emotions are (a special kind of) perceptions (see, e.g., James 1884; Tappolet 2000; Prinz 2004). ‘Weak perceptualism’, by contrast, states that emotions are merely analogous to perceptions (see, e.g., de Sousa 1987; Elgin 1996; Goldie 2000; Johnston 2001;
Does it mean that emotions can be receptors while some argue that emotions are only apparently like receptors?

>(Page 3, 1st paragrapgh) Perceptual and judgemental theories share the core idea that emotions are cognitive states with an intentional content that represents the world as being a certain way and can, therefore, be assessed for correctness.
What the fuck does "intentional content" mean?
Is "assessed for correctness" the big brained version of "It's likely right"?

>(Page 6, 6th paragraph) Emotions seem to depend much more strongly on certain characteristics of the subject experiencing them than perceptions do
Does this mean that the subject that's suffering from certain emotions are more likely to have a unique experience because some characteristics of the subject may influence itself, than perceptions?

>> No.10320834

>assessed for correctness
cognitive states/emotions assess the world for correctness, ie, they try to perceive reality as objectively as possible, but states/emotions offer varying degrees of subjective reality

the other two are similar

>> No.10320981

I'm not sure but i think those two values are just the domain, what you are asked is the tangent vector as a function of t (derivative of j component, derivative of k component), normalized

>> No.10321012

So what would the limits be for the arc length

>> No.10321026

The two values given between [ ]

>> No.10321030

This is going to give a really disgusting answer isn’t t

>> No.10321040

The answer is gonna be simple, maybe the integral you have to go through will be disgusting

>> No.10321226

Alright. I literally cannot get the answer.

>> No.10321234
File: 8 KB, 455x125, Capture.jpg [View same] [iqdb] [saucenao] [google] [report]

I know that I need to integrate dr/dt to get the r(t). but what do I do with the vector?

>> No.10321403
File: 1.15 MB, 2827x935, 20190123_225944.jpg [View same] [iqdb] [saucenao] [google] [report]

How can I prove that this series does diverge? I know that the ratio and root test will give me 1 as an output and therefore do prove jack shit and that I gotta have to use a minor series like e^(1/k) but how do I go further then? Is there a lemma that states how e does behave kn a series when the exponent is positive and ymaller than 1?

>> No.10321660
File: 106 KB, 480x600, jokes_shes_not_24_shes_1800_years_old.jpg [View same] [iqdb] [saucenao] [google] [report]

Why isn't there a piece of software that converts old PDFs into latex ?

>> No.10322128

Hey I plan to take the SAT and I am using Khan academy. What math grades should I master before taking the test?

>> No.10322194
File: 13 KB, 600x337, rms-am-gm-hm-inequality-blog.png [View same] [iqdb] [saucenao] [google] [report]

Read "A Tansition to Advanced Mathematics" and practice solving problems that demand you to think outside the box

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