Leave these fields empty (spam trap):
You can leave this blank to post anonymously, or you can create a Tripcode by using the float Name#Password
A subject is required when posting a new thread
[*]Italic Text[/*]
[**]Bold Text[/**]
[~]Taimapedia Article[/~]
[%]Spoiler Text[/%]
>Highlight/Quote Text
[pre]Preformatted & Monospace text[/pre]
1. Numbered lists become ordered lists
* Bulleted lists become unordered lists


Community Updates

420chan now supports HTTPS! If you find any issues, you may report them in this thread
Discrete Math and Counting by Martin Chashway - Tue, 21 Oct 2014 01:39:18 EST ID:vbQtHDF1 No.14432 Ignore Report Reply Quick Reply
File: 1413869958872.jpg -(23176B / 22.63KB, 250x346) Thumbnail displayed, click image for full size. 23176
Hi /math/, I've got a question regarding counting in Discrete Mathematics. The textbook I have, "Discrete Mathematics With Ducks," is truly garbage and not helpful at all when it comes to... anything. http://www.amazon.com/product-reviews/1466504994/ref=acr_dpx_hist_1?ie=UTF8&filterBy=addOneStar&showViewpoints=0

The question I'm on asks:
How many positive integers solutions are there to the equation y1 + y2 + y3 + y4 + y5 + y6 = 13?

I need some help with this. After break I'm a bit lost. This is under the section of Combinatorial problems, and we've been using the Principle of Inclusion and Exclusion as well as this "stars and bars" technique (I'm not sure if anyone is familiar with this, it might just be my god-awful textbook). So ideally the problem could be solved that way. Thanks.
Esther Sengerford - Tue, 21 Oct 2014 10:52:03 EST ID:Dk8yywxc No.14433 Ignore Report Quick Reply

I don't know about stars and bars but here is how I would think about this.

This problem is like trying to put 13 balls into 6 boxes with at least one ball in each box. Put a ball in each box, so there are 13-6= 7 balls remaining. You can distribute the remaining 7 in C(7+6-1,7)=C(12,7)=792 different ways to do it. The reason there is a -1 is because we don't want 0 to be included.
Basil Gesslepark - Fri, 31 Oct 2014 19:17:48 EST ID:dJKFjM4J No.14460 Ignore Report Quick Reply
Stars and bars? Just imagine a whole bunch of numbered blocks, 1 .. N. You wrote down 5 plus signs. We're going to remove 5 blocks from the N. This will allow removing 5 consecutive from the left, that's okay for now. The spacing between the blocks indicates the grouping of the integers (so an island of 5 blocks: y_k = 5). The only trouble is you specified positive integers, so we should eliminate all the solutions containing 0.

First, how big is N? N should allow for 13 blocks after removing 5, so N = 18.

So the answer is less than (18 5).

Instead of adding up to 13, we could just distribute a 1 to each y_k and add up to 13 - 6 = 7. So (7 5) would represent all the ways to introduce splits in the remaining 7 numbered blocks to distribute them uniquely to y1..y6.

(7 5) = 42, so the answer is 42? It's either 792 or 42, who knows.

Refreshing math knowledge. by Ian Tootson - Wed, 29 Oct 2014 11:54:18 EST ID:GCILLCAz No.14456 Ignore Report Reply Quick Reply
File: 1414598058334.jpg -(49723B / 48.56KB, 1000x728) Thumbnail displayed, click image for full size. 49723
I'm a undergraduate math major who has been out of college for about 2 years. I want to go back to uni but I am extremely rust on my higher level math skills. What tools or resources could I use to revive my mathematics knowledge? This is where my poor note taking has taken its toll.
Should I just use math GRE subject test practice books or do you know of any thing that will help. I am not looking to relearn like kahn academy just practice tests for calculus, linear algebra, multuvariate, and complex.
Thomas Bepperkit - Thu, 30 Oct 2014 11:54:13 EST ID:Dk8yywxc No.14458 Ignore Report Quick Reply

If you don't remember it and aren't taking classes yet, buy some positively reviewed textbooks. Work through them and do some exercises too. Don't forget to do a couple of exercises!

A little bit of google searching should find you some books that people generally regard as good. Don't worry if you work through them slowly, just keep at it every day.
Alice Bardwill - Fri, 31 Oct 2014 12:07:00 EST ID:Ov5dnuCH No.14459 Ignore Report Quick Reply
For calculus just pirate a copy of the Stewart textbook and go through it. It's your standard plug n chug textbook and a huge number of universities use it so it'll put you in good stead for when you're finally back. If you get stuck you can always supplement with the internet. It goes all the way up to multivariable calc, vector calc etc.

Same for linear algebra really. The book we use is "Linear Algebra - A Modern Introduction". Again it can be pirated online.

How do I prove this? by Edward Lightford - Sun, 26 Oct 2014 11:49:57 EST ID:BH6DA7ss No.14443 Ignore Report Reply Quick Reply
File: 1414338597548.png -(800902B / 782.13KB, 1192x702) Thumbnail displayed, click image for full size. 800902
Can anybody help me with this problem?

let f(n)= sum (from i=2 to n) 1/(i ln(i)
Show that f(n) = Θ(ln(ln(n))
Edwin Brocklewell - Tue, 11 Nov 2014 13:41:05 EST ID:qABD7ibX No.14477 Ignore Report Quick Reply
∑1/(i*ln(i)) ≃ ∫dx/(x*ln(x)) = ∫1/x 1/ln(x) dx
Let u=ln(x), du=dx/x
∫ 1/u du = ln(u) = ln( ln(x) )

Calculus by cornelius - Sat, 23 Aug 2014 17:06:36 EST ID:3fml9jmh No.14304 Ignore Report Reply Quick Reply
File: 1408827996393.jpg -(5682B / 5.55KB, 100x143) Thumbnail displayed, click image for full size. 5682
Anybody here recommend any books that are good introductions to calculus? I'm an idiot when it comes to anything beyond geometry and basic trig.
3 posts omitted. Click Reply to view.
Caroline Soffingkuck - Tue, 02 Sep 2014 23:01:27 EST ID:WLG9+3r6 No.14345 Ignore Report Quick Reply
> plus a semester of linear algebra.


if i had this years ago..
Archie Worthingfield - Sun, 07 Sep 2014 18:22:36 EST ID:xvgqavvT No.14353 Ignore Report Quick Reply
Sheldon Axler's Precalculus is the best out there I find. http://precalculus.axler.net/
He assumes you know/remember nothing about trig and goes from there, good introduction.

Khan Academy comes under fire from other mathematicians occasionally for presenting inaccurate info. Not a week goes by on HN where somebody doesn't call them out for shoddy lessons (which to their credit they clean up)
Phyllis Wullywill - Wed, 08 Oct 2014 00:08:44 EST ID:y2Fx3geS No.14411 Ignore Report Quick Reply
Any more like him besides khan?
Sidney Hammlegold - Thu, 23 Oct 2014 21:26:09 EST ID:IcAEoDAz No.14436 Ignore Report Quick Reply
Based Paul

Edwin Brocklewell - Tue, 11 Nov 2014 13:54:42 EST ID:qABD7ibX No.14479 Ignore Report Quick Reply

Is there anything to see here? by Graham Chacklestidging - Sun, 19 Oct 2014 12:29:00 EST ID:FgPWXR9d No.14421 Ignore Report Reply Quick Reply
File: 1413736140638.jpg -(80374B / 78.49KB, 640x960) Thumbnail displayed, click image for full size. 80374
Alice Hodgebanks - Sun, 19 Oct 2014 18:04:04 EST ID:uspvjvJI No.14422 Ignore Report Quick Reply
no, it's just your imagination.
Emma Pittshit - Tue, 21 Oct 2014 00:08:08 EST ID:hu6SgEj9 No.14431 Ignore Report Quick Reply
well it's like the limit expression of e. I don't get why the (1+ is so important there.

Mathematical logic by Fanny Cicklefatch - Sat, 18 Oct 2014 17:29:26 EST ID:IJ85y6zt No.14418 Ignore Report Reply Quick Reply
File: 1413667766815.png -(106315B / 103.82KB, 320x287) Thumbnail displayed, click image for full size. 106315
Let's say we disprove a set of hypotheses A. Each hypothesis is not as likely as each other to be disproved. How does one account for that? Does one use probabilistic logic to determine how likely each hypothesis is to get disproved? Or does one need to create a new type of logic entirely which gives a 'weight' to each hypothesis - how likely it is to get targeted and disproved?

For example ¬(A ∨ B) |- ¬e. How do we determine which set of hypothesis - A or B, is more likely to get targeted by disproval?
Jenny Cishfield - Sat, 18 Oct 2014 18:52:13 EST ID:Dk8yywxc No.14419 Ignore Report Quick Reply

I don't understand your notation, can you try rephrasing the question? Perhaps with an image?

Do you mean we're trying to prove some statements, and you're asking how likely it is each statement will be proved? If that is what you mean, it really depends on the statements themselves. Some statements are innately unprovable or you may not be able to prove it either way with the assumptions that you have made.
Isabella Guddlelock - Sun, 19 Oct 2014 12:17:01 EST ID:IJ85y6zt No.14420 Ignore Report Quick Reply
Let's say we have ¬(A ∨ B). How do we determine which is more likely to be false: A or B?
Samuel Mollersidge - Mon, 20 Oct 2014 08:43:18 EST ID:MTIV7/tU No.14426 Ignore Report Quick Reply
They are both as likely, since A v B is propositionally equivalent to B v A.
Or is there something I don't get here ?
Phoebe Mundlepin - Mon, 20 Oct 2014 11:03:05 EST ID:Dk8yywxc No.14428 Ignore Report Quick Reply

Lets try putting that into english. What you posted means "Not (A or B)", which could be rephrased as "neither A nor B". So if we have ¬(A ∨ B), we know that both A and B are 100% false.

Using a transformation rule called DeMorgans Law, we can pass the negation over the disjunction to obtain ¬A & ¬B.

If on the other hand the phrase was ¬(A&B), then we know either they are both false or only one of them is false. Using DeMorgans law yields

¬A ∨ ¬B

If you want to "really" find out which one is false, we need more information about A and B themselves.

RNGs by Caroline Crummleville - Fri, 10 Jan 2014 00:40:43 EST ID:G4lGyG09 No.13597 Ignore Report Reply Quick Reply
File: 1389332443035.jpg -(34265B / 33.46KB, 400x329) Thumbnail displayed, click image for full size. 34265
Anyone know of a way to ACCURATELY predict dice rolls for RNGs? Specifically I am looking to predict dice rolls for Blood Bowl: Chaos Edition.

There used to be a program that did it but since then they made a patch and moved the algorithm and seeds to the sever side.

Anyone got ideas on how to do this?
5 posts omitted. Click Reply to view.
Samuel Secklesat - Wed, 22 Jan 2014 12:10:17 EST ID:G4lGyG09 No.13630 Ignore Report Quick Reply

It uses a mersenne twister with the seeds kept server side.
Jack Handermen - Fri, 24 Jan 2014 11:00:18 EST ID:sPd/0oB/ No.13631 Ignore Report Quick Reply
It's hard to do, really. The whole point of moving the seed to the server side is to make it almost impossible...

You could keep a sequence of random number (the original 32/64 bits sequence) fresh from the server, check how the seed is choosed and try to brute force the seed from here. For instance if the seed is a timestamp (it's common), pick several timestamp around the one you think is likely.
Even then you would need to keep track of how fast the RN are produced (is the server giving RN from the same seed to everyone?).

You need to decompile the server binaries to do that. If you don't have them, it's a lot harder.

You should ask this on /tinfoil/.
Ebenezer Movinghall - Mon, 27 Jan 2014 05:07:56 EST ID:DFb+IUXc No.13638 Ignore Report Quick Reply
Why not?
Shitting Grimstock - Mon, 27 Jan 2014 13:46:27 EST ID:pJYYYREs No.13639 Ignore Report Quick Reply
1390848387982.png -(145633B / 142.22KB, 1920x1080) Thumbnail displayed, click image for full size.
There's nothing that some social engineering and espionage can't solve, Gentlemen.
Mangus von Vaginakowski !qrtrbnpccM - Wed, 08 Oct 2014 20:56:00 EST ID:K3z3WKaF No.14414 Ignore Report Quick Reply
Without access to the server or an exploit the DEVs fucked up on and left that allows you to do the [P]RNG, you're SOL.

Trig sub by Hedda Snodham - Tue, 07 Oct 2014 22:22:34 EST ID:9Czw1b2g No.14410 Ignore Report Reply Quick Reply
File: 1412734954064.gif -(2075656B / 1.98MB, 264x204) Thumbnail displayed, click image for full size. 2075656
Hey niggas i got this integral here: dx/((radx)(x+1))
some help setting up the trig sub would be greatly appreciated.
Cornelius Dartman - Wed, 08 Oct 2014 10:22:23 EST ID:Gw2IN3ba No.14412 Ignore Report Quick Reply
You need to perform two substitutions. First use x = sin^2(u). Then use v = sin(u).
Cornelius Dartman - Wed, 08 Oct 2014 10:38:17 EST ID:Gw2IN3ba No.14413 Ignore Report Quick Reply
Wait, scratch that. Just use x = u^2. The end result has inverse trigonometric form, but the substitution doesn't need to be trigonometric.

Relearning math by Wesley Blatherson - Wed, 10 Sep 2014 08:12:53 EST ID:D/oQWr2Y No.14356 Ignore Report Reply Quick Reply
File: 1410351173283.jpg -(82220B / 80.29KB, 504x470) Thumbnail displayed, click image for full size. 82220
I've always been naturally bad at math, I failed algebra 2 twice in highschool because I just couldn't grasp the concepts fast enough. My sister who's a freshman in highschool asked me to help her with her homework, and I didn't know JACK SHIT.

I'm 20 and going to community college for a few courses while I work this upcoming spring, I don't plan to take math right away but is there some sort of program/books that will let me relearn math right from the beginning?
3 posts and 2 images omitted. Click Reply to view.
Hannah Penningcocke - Fri, 19 Sep 2014 11:15:59 EST ID:AJrEUkAQ No.14369 Ignore Report Quick Reply
I would love to help you with basic algebra/algebra 2!! I highly suggest taking math from the beginning, as you have quite a few semesters to make up to college-level courses if you're starting from the beginning. If you still won't do that, I suggest taking some time and learning some stuff on your own. http://khanacademy.com/ is an amazing resource; it's interactive, polished, and familiarizing yourself with stuff there will prepare you for doing mathematics on a computer, which you probably haven't done much since you haven't done math since high school.
Archie Goodman - Wed, 24 Sep 2014 13:12:32 EST ID:a8Tw8LvY No.14378 Ignore Report Quick Reply
>failed algebra 2 twice
I did 3 times, mostly because 2nd semester of algebra 2 is kinda bullshit. Now I'm in 3rd year engineering and I did Calc 3 a year ago
Rebecca Chorringfuck - Fri, 03 Oct 2014 11:45:44 EST ID:Z+iZvwQ7 No.14405 Ignore Report Quick Reply
Any site for physics? I'm taking capacitors and shit like that, electricity and magnetism. Need a good website for this stuff, preferably video. Youtube and khanacademy are insufficient.
Hedda Charringville - Fri, 03 Oct 2014 17:08:10 EST ID:V2nhYpJ2 No.14407 Ignore Report Quick Reply
MIT lectures
Might or might not be the correct section of the site, but if your answer cannot be found here you are either not looking close enough or undestanding it's in front of you.
Clara Crebblechodging - Fri, 03 Oct 2014 17:26:19 EST ID:xvgqavvT No.14408 Ignore Report Quick Reply
Re-learning math:

1) Lial's Basic College Math

This covers Kindergarten - Algebra. All the editions are the same so pirate/buy any of them.

2) Serge Lang's "Basic Mathematics" is great and will cover all you need to go into a rigorous theory based college math class. http://www.amazon.com/Basic-Mathematics-Serge-Lang/dp/0387967877/ref=sr_1_1?ie=UTF8&qid=1412284774&sr=8-1&keywords=serge+langs+basic+mathematics

There's also "No Bullshit Math" which does the same as Serge's book: http://minireference.com/ and Sheldon Axler's "Precalculus" which does the same.

I liked Serge's book. It's written by a Mathematician who doesn't hand hold or do anything else except teach you basic math from an advanced standpoint.. so you learn proper terms of everything and actually understand wtf is going on.

For Calculus I did MIT OpenCourseware 18.01 (Single) and 18.02 (Multi). There are no books, just lectures and assignments. After I did them I wanted to explore proofs more so did 18.014 and 18.024 (Both on the open courseware site). Basically all it consists of is doing a rigorous Calc book where you do a lot of proofs. I did them all in Scheme (because I was also trying to learn how to code). http://ocw.mit.edu/courses/mathematics/18-014-calculus-with-theory-fall-2010/ contains course notes by Munkres!! Awesome.
Comment too long. Click here to view the full text.

negative binomial help by Clara Fubblewill - Fri, 03 Oct 2014 15:03:16 EST ID:Aql4bjnf No.14406 Ignore Report Reply Quick Reply
File: 1412362996183.png -(3140B / 3.07KB, 458x381) Thumbnail displayed, click image for full size. 3140
I'm trying to get the variance for hypergeometric discrete random variable without using the moment generating function and am having a lot of trouble.. I started with V(X)= E(X^2) - E(X)^2 and can get E(X)^2 but can't get E(X^2). Then someone suggested I try E(X(X+1)) but I don't understand how to do that.... Any help?

Clarification on velocity vector and acceleration by Fanny Nendlefetch - Mon, 29 Sep 2014 17:57:44 EST ID:dfurG/DB No.14392 Ignore Report Reply Quick Reply
File: 1412027864973.gif -(426031B / 416.05KB, 667x488) Thumbnail displayed, click image for full size. 426031
The problem is below; what my question is, is do I need to know t or what? If I don't, then what do I do and if I do need it, how do I find it?

At a certain moment, a particle moving along a path has a velocity v=<3,2,1> and a=<0,5,2>. Find T, N and the decomposition of a into tangential and normal components.

If I had a parametrized function for v I'd be good, but I don't because I don't know t...
Any help?
Fanny Nendlefetch - Mon, 29 Sep 2014 19:38:38 EST ID:dfurG/DB No.14393 Ignore Report Quick Reply
fac u op
Nell Foshfield - Wed, 01 Oct 2014 06:50:01 EST ID:Gw2IN3ba No.14402 Ignore Report Quick Reply
If by t you mean time, they don't provide that information and there is no way to deduce it. T here is kinetic energy and N is the normal force, yes? All you need to find T is the velocity and the mass (I assume the mass was provided earlier). Because the velocity must be tangential to the path at the point under consideration, you can use this to find the tangential and normal components of a. And the normal force is just the normal component of a scaled by m.
John Fendernidge - Wed, 01 Oct 2014 22:27:34 EST ID:kDYSaBHq No.14404 Ignore Report Quick Reply
To find tangential acceleration just project the a vector onto v

a_tan = a dot v/||v||

Then a_norm = a - a_tan

yay math

Help, what the fuck is P? by Fuck Donningdale - Thu, 25 Sep 2014 01:46:11 EST ID:aQ2ap22j No.14379 Ignore Report Reply Quick Reply
File: 1411623971598.png -(17447B / 17.04KB, 753x627) Thumbnail displayed, click image for full size. 17447
How do I solve these?
Or what are the solutions?
3 posts omitted. Click Reply to view.
Lydia Pengerwone - Sun, 28 Sep 2014 17:55:22 EST ID:V2nhYpJ2 No.14390 Ignore Report Quick Reply
Actually because the function and boundaries are linear, the minima & maxima are at the intersections.
Lydia Pengerwone - Sun, 28 Sep 2014 17:58:00 EST ID:V2nhYpJ2 No.14391 Ignore Report Quick Reply
No wait, it can't be.
P = 10 - x - y;
f = { -10 < x < 10; -10 < y < 10 }
So what are the actual criteria for the minima & maxima being at the boundary and/or the intersections?
Martha Donkinherk - Mon, 29 Sep 2014 23:01:21 EST ID:umZ//85N No.14394 Ignore Report Quick Reply
1st one,
x-y <=4

use above two equations, solve for y
y<= 6 - x
y >= x - 4
y>= 0
since x <=5, and x-4 <= y, then the maximum of y is 1, thus we know
0<= y <= 1
at this point i think x is unbounded, meaning that P has no minima
but the maximum is x = 5 and y - 1 so Max P = 20
Martha Donkinherk - Tue, 30 Sep 2014 00:07:18 EST ID:umZ//85N No.14396 Ignore Report Quick Reply
never mind im retarded this isnt right
John Fendernidge - Wed, 01 Oct 2014 22:24:51 EST ID:kDYSaBHq No.14403 Ignore Report Quick Reply
lol you were right the first time. For your example the maximum is at one of the corners, x=y=-10

<<Last Pages Next>>
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Report Post
Please be descriptive with report notes,
this helps staff resolve issues quicker.