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420chan is Getting Overhauled - Changelog/Bug Report/Request Thread (Updated July 26)

fertilizer question

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- Fri, 22 May 2015 19:43:11 EST YCs1tF7z No.14741
File: 1432338191011.jpg -(51219B / 50.02KB, 720x960) Thumbnail displayed, click image for full size. fertilizer question
Hello /MATH/ I have a quick question for you to help me out with if that's cool.
Basically I just need to know how much fertilizer 20-4-8 would be in a 100lb bag
Phineas Hepperdock - Wed, 27 May 2015 23:45:30 EST Jz+dW0dw No.14755 Reply
Those are percentages.

Surely you know what a percent is.

<3 <3

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- Wed, 18 Jun 2014 06:38:10 EST Fj/YvlCk No.14096
File: 1403087890404.jpg -(15466B / 15.10KB, 350x350) Thumbnail displayed, click image for full size. <3 <3
I love maths and I love you <3

Share whatever proof, trick, theorem, mathematical tool, number, or other maths-related stuff you like in this thread.

I like e. It's always felt a bit "blue" for me, you know 2.7182818284590452353... A nice deep blue.
67 posts and 19 images omitted. Click View Thread to read.
Caroline Brebbermag - Fri, 15 May 2015 20:25:48 EST K8qJv5EF No.14733 Reply
1431735948243.gif -(715742B / 698.97KB, 440x330) Thumbnail displayed, click image for full size.

Hmm, to really understand the gravity of the spectral theorem, you'd need to have a pretty firm understanding of functional analysis, which in turn requires a firm understanding of linear algebra *and* measure theory.

For measure theory, probably the best beginner's book would be Royden's "Real Analysis", 3rd edition. Very clear language, motivates the study, etc. Be ready for some abstraction, though: measurable sets and functions are ill-behaved to say the least.

Once you understand the Lebesgue Integral, you'll be ready for functional analysis. There are many fantastic texts on the topic, but if you're *only* interested in learning spectral theory, you might want to try "Theory of Linear Operators in Hilbert Space," by Akhiezer and Glazman. This is a Dover book, and therefore very cheap. It covers everything from the basics of functional analysis (on inner product spaces) to the full spectral theorem for self-adjoint operators.

If you want a basic rundown of the spectral theorem, it basically says that very symmetric operations of certain kinds (like multiplication by a real number [boring] or the second derivative operator [interesting]) can be used to decompose certain vector spaces via an orthonormal basis, i.e. into a coordinate system where each axis is at "a right angle" with each other axis. This allows one to decompose your symmetric operation into a sum of very simple transformations on individual components. Like any other "decomposition" theorem, this is *extremely* advantageous when solving tough problems where these operators play a big role.

As for IBP, when combined with Sobolev spaces, it allows you to transform a second order partial differential equation into an integral equation of sorts. If your original PDE was linear, your integral equation gets alllll sorts of special properties (bilinear forms are what they become). This allows for really interesting theorems from functional analysis, like the Lax-Milgram theorem or the spectral theorem, to become immediately applicable to solving, or at least guaranteeing a solution to, your PDE. You *must* have Sobolev spaces for this approach to be sound, however.
Ian Noffingdock - Tue, 19 May 2015 15:35:08 EST NCaB2rkH No.14738 Reply
You've provided some great resources to look into here and a clear path forward Brebbermag, I thank you for it.
Caroline Murdbury - Wed, 27 May 2015 04:01:40 EST 96SVbDTc No.14753 Reply
This is along the same lines as my little trick for squaring, will use the same number. I don't even remember where I got it from, I think my calc 3 teacher squared some big number with it and I thought it was really elegant.


As for my favorite thing, the bisection method of root finding is up there. Just a really really beautiful and simple way of looking at the problem. The idea of "just split an interval in half and figure out which half has the root in it, repeat" is just really neat to me.

Helpless dumbfuck calling for help

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- Mon, 04 May 2015 16:43:13 EST 3dz0uQ7J No.14724
File: 1430772193140.gif -(2314B / 2.26KB, 388x298) Thumbnail displayed, click image for full size. Helpless dumbfuck calling for help
Is a horizontal or vertical line that expands to infinity it's own asymptote? Or is this in this case not applicable and a really dumb question?
Phineas Hecklesot - Tue, 05 May 2015 10:18:46 EST xOOOxXVr No.14725 Reply
An asymptote is defined as a value that is approached but never reached. Y=3 reaches Y = 3, so it's not its own asymptote

nice question though
Reuben Chacklefield - Sun, 17 May 2015 06:24:17 EST WtAxPZi7 No.14734 Reply
1431858257260.png -(246045B / 240.28KB, 444x604) Thumbnail displayed, click image for full size.
tl;dr not really but I can prove otherwise

So consider the horizontal line y (x) = 3 i.e. y is independent of x, so for all values of x, y is always 3.
If x/x = 1,
then y (x) = 3 = 3*1 = 3x/x
It would still give you a horizontal line, but at x = 0 shit fucks ass.
You can then repeat this idea with other values like (x-1)/(x-1) = 1 so you get a "hole" at x=1, so on and so forth. Repeat this for all values of x and insert it into the equation then your line will be asymptotic to itself.
Shit Bottingbire - Sun, 17 May 2015 13:24:26 EST xOOOxXVr No.14737 Reply

An asymptote is a discontinuity, but not all discontinuities are asymptotes. What you just described is a function that is not continuous at all integer values of x, but not one with an asymptote.

I would also tend to argue that y = 3(x/x) is a different function from y = 3 simply because it returns different results

How can I relearn math?

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- Sun, 26 Apr 2015 16:13:04 EST L+X0k1Ap No.14703
File: 1430079184240.jpg -(9197B / 8.98KB, 267x181) Thumbnail displayed, click image for full size. How can I relearn math?
Hello /math/. I have retrograde amnesia.
I've forgotten math essentially, so much so that my abilities have regressed to that of a high school freshman.
Where and how do I relearn what I've forgotten? I've lost my job because of this.
4 posts and 2 images omitted. Click View Thread to read.
Barnaby Fizzletetch - Sat, 02 May 2015 19:18:23 EST Hj/F401x No.14716 Reply
I've been in the exact same situation. Didn't like math in HS, didn't do it for years afterward. When I started taking classes again, I got owned hard.
Fast forward to the day before yesterday and I feel like I did pretty good on the back-to-back midterms I took on Fourier analysis + linear ODEs and algorithms (which is proof-heavy).

The same boiling water that softens the potato hardens the egg.
Martin Dribberdark - Sat, 09 May 2015 01:52:04 EST YlDX0MWs No.14727 Reply
My memory has always been shit, but it turned out to work in my favor for maths because I couldn't just memorize everything, I ended up having to derive everything, and re-derive it and re-derive it sometimes, until it made sense in an I guess "intuitive" level. Turns out this is a pretty good way of learning math, if a bit "slow".

My advice is to start MORE basic than you think. If I say "learn about fractions" and your reaction is "no that's too easy I want to start higher", I would suggest not to skip it. Spend a little bit actually working problems so you definitely have a very solid foundation. When I tutored calculus, there were students who got all frazzled at when where and how (not to mention why) they could "cancel out" a numerator and denominator, so their learning got held up because somewhere along the way they were like "yeah yeah ok whatever got it"
Basil Giffingford - Mon, 11 May 2015 10:33:10 EST bG7/Mgyv No.14731 Reply
Buy/torrent the book "Basic Mathematics" by Serge Lang. It's highschool and precalc but written from the perspective of a mathematician so you get a rigorous logic and analysis course out of highschool math instead of just being a calculator.


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- Sun, 03 May 2015 14:03:43 EST zDln8d4D No.14718
File: 1430676223389.jpg -(1186244B / 1.13MB, 2592x1936) Thumbnail displayed, click image for full size. Soo
denominators dont cancel eachother out ,right? Tf do i do here?
2 posts and 1 images omitted. Click View Thread to read.
Sophie Perringchure - Sun, 03 May 2015 20:11:51 EST hudlvJsh No.14721 Reply
Looks right to me
Is the equation supposed to equal something? are you trying to solve for a?
Hamilton Fundlebick - Sun, 03 May 2015 21:18:36 EST zDln8d4D No.14722 Reply
Nah I fired it out
I was supposed to multiply the 3s

Discrete Maths: Video Courses

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- Thu, 23 Apr 2015 20:57:44 EST Y+QSKjuy No.14700
File: 1429837064194.jpg -(205184B / 200.38KB, 640x480) Thumbnail displayed, click image for full size. Discrete Maths: Video Courses
Hey guys,

I'd really like to learn discrete maths, preferably starting with some video series. Ones that would cover the subjects well in depth, rather than giving brief overviews. I will turn to books after that, it's just that having an actual teacher on such media is for me way more stimulating and makes me feel more involved.

Could anyone be kind enough to recommend such video serie(s) that go well in depth for each subject?

That would be greatly appreciated, thanks!
Nigger Sungerforth - Thu, 30 Apr 2015 05:00:01 EST i84x+n57 No.14713 Reply
A while back, I torrented a lecture series by Arthur T. Benjamin in order to teach myself discrete math. I found them pretty helpful. Give 'em a try; they shouldn't be too hard to find.
Nigger Sungerforth - Thu, 30 Apr 2015 06:55:06 EST i84x+n57 No.14714 Reply
1430391306245.png -(116171B / 113.45KB, 300x200) Thumbnail displayed, click image for full size.




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- Tue, 28 Apr 2015 00:24:22 EST eI+mFgPX No.14708
File: 1430195062832.jpg -(1885217B / 1.80MB, 3264x1836) Thumbnail displayed, click image for full size. finalss
I have my analysis final Wednesday. I'm redoing past tests and I cannot figure out number 4 part a! Some kind soul please help!
Thomas Sommerville - Tue, 28 Apr 2015 00:39:31 EST qz3c7Bt+ No.14709 Reply
1430195971688.gif -(1338B / 1.31KB, 318x52) Thumbnail displayed, click image for full size.


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- Sun, 26 Apr 2015 03:31:01 EST 6wsrD9dK No.14701
File: 1430033461840.jpg -(77327B / 75.51KB, 1150x143) Thumbnail displayed, click image for full size. HALP.
I'm allowed to ask for help here?

I haven't done maths since high school and I cannot work out why my final projection total is different if you work it out as a row (As in with the totals of the year) or if you work it out as a column (as in the totals revenues of each market).

This is obviously a pretty newby question but if its any community consolation I help out newbies on boards I know shit about. Thanks /math/
Hamilton Fellerbuck - Sun, 26 Apr 2015 12:40:31 EST qz3c7Bt+ No.14702 Reply
I don't know what the hell you're talking about but the "Residential Services Total" for 2008 is not equal to the sum of the first three rows in "2008 Projection". This disagrees with the way 2005, 2006, and 2007 "Residential Services Total" are being computed. Are you doing this by hand?

Have mercy on my undeserving soul // Pass Calc Exam

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- Mon, 02 Mar 2015 01:53:56 EST oIF65CiW No.14625
File: 1425279236506.jpg -(136105B / 132.92KB, 460x345) Thumbnail displayed, click image for full size. Have mercy on my undeserving soul // Pass Calc Exam
Look, I'll get right to the point.

I'm smart, but I put no effort into school. It's fucked up, and I'm sorry.

I need to pass my 2nd Calc 1 exam, which covers limits, differentiation, implicit differentiation... basically all of Chapter 2 in the standard Stewart Calculus book, and that exam is on Wednesday around 6pm.

How can I best prepare for this exam? I am able to grasp concepts, I understand math up until Calc, and limits/differentiation fairly intuitively, but I fail in the details. I really haven't kept up to speed with this class because, as previously stated, I'm a jackass.

Just... have mercy on my soul, /math/ friends. I am trying to clean my act up.
4 posts omitted. Click View Thread to read.
Sidney Suzzleson - Fri, 27 Mar 2015 21:47:51 EST FF4db3LF No.14671 Reply
Seconding this. I'm in Cal 3 right now, and it's nothing to worry about. Cal 2 can be rough the first time around, though.
Beatrice Claywater - Sat, 28 Mar 2015 19:32:07 EST uBbxSpMx No.14674 Reply
I'd say look over the past papers right away so that you have an idea of what kind of questions you may be asked. Practice those questions over an over again, do them looking at your notes so you get how to do the questions. Then do all that other stuff.
Phineas Suffinglock - Thu, 16 Apr 2015 15:25:59 EST xwcXgACR No.14698 Reply
1429212359575.jpg -(110438B / 107.85KB, 1280x800) Thumbnail displayed, click image for full size.
Myself and my group of friends consider ourselves, "smart" but my friend and I went through an enormous shift during our first encounter with calculus. Part of it was realizing that our algebra skills, as developed by the education system, were sub-par and we had to take the reigns to make sure our mathematical life was in order. The second thing was that we went through our first mathematical "growing pains", alluding to the idea of mathematical maturity.

Besides doing practice problems, you might want to soak up and wonder about what you're actually seeing. The feeling you get when you realize another level of generalization can be pretty dramatic. For example, realizing that you can construct mathematical objects from thin air and apply calculus tools to them, as long as you do this properly. It's the first time you're asked to be creative mathematically instead of just remembering things. This leads me to my next point.

When you're studying math the best thing you can do is collect and understand the hard facts relating to what you're studying. Theorems, differentiation rules, etc. The facts you know will determine what moves you can confidently make when you don't have any references around you. The depth of your imagination, as I referred to earlier, will determine what moves will occur to you. It doesn't matter if you have all the facts if you can't use them. My impression is people generally feel insecure when they do math, because it seems like a very authoritative subject. You might try something, "your way" only to be told that's not right. The only way to get fluent in math is by making creative decisions motivated by facts and then being reassured when you find out you're right.

Do the homework, but don't be afraid to sling dick and do every problem you can get your hands on. The problems that take an entire day to solve can be the most rewarding because it's likely not computationally difficult, it's conceptually difficult. If you have all the facts and still can't do the problem quickly, then you're probably going to experience the kind of mind expansion required to get to the next level.

I think I was just like you when I took calculus. At the end of the day, your struggle will pay off, no matter how well you do or don't do. It just matters that you show up and have enthusiasm for what you're doing.

what is the two consecutive number?

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- Wed, 15 Apr 2015 10:35:58 EST iHlPHeD4 No.14692
File: 1429108558063.png -(115227B / 112.53KB, 400x636) Thumbnail displayed, click image for full size. what is the two consecutive number?
found this puzzle on the internet, and it drives me crazy. say, you got a number that we call "A", "A" is divisible with all the numbers between 1 and 10 001. excluding two consecutive numbers in that range. We dont care about "A", we want to know the two consecutive number. How should i start this?
1 posts omitted. Click View Thread to read.
Phyllis Drocklewore - Thu, 16 Apr 2015 05:03:44 EST qz3c7Bt+ No.14694 Reply
Oops. Let the least common multiple be 'x'. Your 'a' is then x /((p)(p+1)).
Doris Clupperstock - Thu, 16 Apr 2015 05:11:36 EST TG1mst7r No.14695 Reply
You know it has to be the largest power of some prime factor of lcm(2,3,...,10001) and ±1 of it being a prime. If ±1 is even then you already have the factors in A so the prime^n had to be 2^n. Log_2(10001)≈13 so we need 2^13±1 to be prime. Since 2^m≠13 for any integer m by some number theory theorem 2^13+1 can't be prime. Thus if it's possible at all, 2^13-1 must be prime and wolfram alpha says it is.
Phyllis Drocklewore - Thu, 16 Apr 2015 14:20:25 EST qz3c7Bt+ No.14697 Reply
The theorem you're describing is Mersenne's conjecture-- it turned out to be false.


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- Wed, 18 Dec 2013 07:58:21 EST CGJx9sbH No.13496
File: 1387371501271.jpg -(457945B / 447.21KB, 1080x1920) Thumbnail displayed, click image for full size. Might
I did some math right now overly blazed. I hope I did good, mathgods.
I really hope I did well.
10 posts and 3 images omitted. Click View Thread to read.
Nigger Dubberdet - Fri, 23 Jan 2015 15:12:27 EST OlFjx/Q0 No.14573 Reply
Copypasta from wiki on Paul Erdős:

>After 1971 he also took amphetamines, despite the concern of his friends, one of whom (Ron Graham) bet him $500 that he could not stop taking the drug for a month.[17] Erdős won the bet, but complained that during his abstinence, mathematics had been set back by a month: "Before, when I looked at a piece of blank paper my mind was filled with ideas. Now all I see is a blank piece of paper." After he won the bet, he promptly resumed his amphetamine use.
Priscilla Crallerfidging - Sat, 24 Jan 2015 16:35:06 EST jEbtLayo No.14575 Reply
That's bullshit. When I'm tripping I can't do math worth shit. The major problem is short term memory impairment and lack of focus. I'm sure you could do a very low dose of lsd and force yourself to do some work but there really isn't any reason to.
hybridgrace - Thu, 09 Apr 2015 19:26:45 EST A1LnfKBL No.14688 Reply
1428622005863.jpg -(23028B / 22.49KB, 410x369) Thumbnail displayed, click image for full size.
LSD is ideal for finding novel solutions and perspectives to problems that you're already familiar with, I assume this applies to mathematics as well

Cryptography where to start

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- Tue, 24 Mar 2015 06:01:37 EST ZkV6uFpl No.14663
File: 1427191297762.jpg -(6693B / 6.54KB, 550x275) Thumbnail displayed, click image for full size. Cryptography where to start
I need recommendations for books that teach a solid theoretical base of cryptography, and also what previous knowledge i need?
Reuben Bardfield - Mon, 30 Mar 2015 03:06:15 EST UqThtfYr No.14676 Reply
Lot's of linear algebra and number theory. Here's a sample paper this cryptographer uses Lattice reduction to do analysis https://www1.lip6.fr/~joux/pages/papers/ToolBox.pdf

You need "mathematical maturity" which means you can read and write proofs, and you can figure out mathematical notation if given a key for what the symbols mean. Spivak's Calclulus is a good book to get said maturity, so is "How to Solve it" or "How to prove it" (look them up on Amazon).

There's some intro cryptography courses around http://bryanpendleton.blogspot.ca/2012/05/comparing-coursera-and-udacity.html
they usually use this book: https://books.google.ca/books?id=1YwIcpDtQPEC (Schneier's first book is too outdated, this version with Ferguson is good).

Or just go through various university calendars and see what kind of information you can find, like lecture notes, recommended reading to look up yourself, ect http://cseweb.ucsd.edu/classes/wi10/cse206a/

Universities consider advanced crypto courses their specialist shit so almost always make them expensive and not open to the public. You should look up whoever was a finalist at the SHA-3 competition and read through the papers (or public comments to NIST) of their analysis http://www.groestl.info/analysis.html where you'll learn how modern cryptographers break each other's shit and thus learn a solid theoretical base.
Doris Clupperstock - Thu, 16 Apr 2015 05:22:05 EST TG1mst7r No.14696 Reply
>I need recommendations for books that teach a solid theoretical base of cryptography

What do you mean by theoretical base? Provable security or the mathematical basis of underlying operations (elliptic curves, algebra, etc)...

"Introduction to Modern Cryptography" by Katz and Lindell for the former
"An Introduction to Mathematical Cryptography" by Hoffstein, Pipher, and Silverman for the latter

Mathematical induction

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- Sat, 28 Mar 2015 19:11:07 EST fghQwkMe No.14672
File: 1427584267069.png -(3736B / 3.65KB, 303x333) Thumbnail displayed, click image for full size. Mathematical induction
Hello /math/ can you guys help me?
I need to prove that these propositions are true for every whole positive N.
does any one know how to solve it ? pls explain how did he arrive at the solution.

A) 2 + 4+ 6 + ...+(4n-2)=2n^2

C)1 + 3 + 6 + .... ( n(n+1) )/2 = ( n(n+1)(n+2) )/6

D) 1/1.2 + 1/2.3 + 1/3,4+ . . . + 1/n(n+1) = n/(n+1)
Beatrice Claywater - Sat, 28 Mar 2015 19:28:32 EST uBbxSpMx No.14673 Reply
A) Test the case where n =1: LHS: 2, RHS 2*(1)^2=2
It works!
Assume it works for k.
Want: works for k+1.
sum to k+1: 2 + 4 +6 + ... + (4k-2) + (4(k+1)-2)
Write the sum up to k as 2k^2. (we're assuming it works)
we get: 2k^2 +4k-2
what does 2(k+1)^2 equal?
It works for k+1!
Now by principle of induction ... ... ...V-allz n in the o'naturelle we just proved blah blah blah

I'm not sure what the homework rules are on this bored. If it says "no homework threads" please delete this thread and take it to http://mathoverflow.net/, I'm sure they'll be more than happy to help
Caroline Hubblechetch - Sun, 29 Mar 2015 02:27:13 EST qz3c7Bt+ No.14675 Reply
1427610433362.gif -(11312B / 11.05KB, 654x366) Thumbnail displayed, click image for full size.
I like these

Quadratic Reciprocity

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- Fri, 13 Feb 2015 08:52:14 EST iRDOjfyp No.14607
File: 1423835534426.jpg -(42733B / 41.73KB, 301x431) Thumbnail displayed, click image for full size. Quadratic Reciprocity
Hey /math/, I've been reading a lot of maths in the last year because I always enjoyed it at school. I'm comfortable with all the maths one might do in high school and bits and pieces of other areas.
I'm told that some proofs for quadratic reciprocity are very beautiful, although I just can't get my head around what it actually IS
Can anyone enlighten me?
2 posts omitted. Click View Thread to read.
Phoebe Bonnerbetch - Wed, 25 Mar 2015 10:22:53 EST HZ1lfOQk No.14666 Reply
(a/b) is real bad notation, if I'm wrong I'd love to hear an argument in favor of it.

Fucking sloppy shit imo.

Way too much gets forgiven by "I'm familiar with it so it's okay"
Whitey Mangerbare - Wed, 25 Mar 2015 16:10:23 EST RzF3HHjt No.14667 Reply
I'm sorry, I was pretty tired last night when I typed it up.

Replace the (d/p) with [d/p], (p/q) with [p/q] and anything else involving (x/p) where x is anything by [x/p].

If you're talking about just in general then I personally don't see it as that much of a problem.
Oliver Sobberchetch - Wed, 25 Mar 2015 21:10:05 EST IaC61I0h No.14668 Reply
i wrote this in another thread on /math/ like a year ago but yeah (a/b) sucks ass and i prefer to do L_b (a) for legendre symbol

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