Search found 130 matches

by Xutar
Tue Apr 20, 2010 12:44 pm UTC
Forum: Mathematics
Topic: Interesting infinite series for phi
Replies: 2
Views: 1195

Interesting infinite series for phi

on the middle of its Wolfram page , this thing pops up: \phi = \frac{13}{8}+\sum_{n=0}^{\infty} \frac{(-1)^{n+1}(2n+1)!}{(n+2)!n!4^{2n+3}} Everything else on the page is understandable, but this seems to come out of left field, and I don't know where to begin Basically, I was...
by Xutar
Tue Mar 16, 2010 2:20 pm UTC
Forum: Mathematics
Topic: easy permutation group problem
Replies: 1
Views: 348

easy permutation group problem

I picked up a copy of "Fearless Symmetry" on a couple recommendations/good reviews and so far I love it. There was one example problem they gave at the end of the section on permutation groups though: Verify the following equality, \sum_{\{a,b,c,d,e\}}:(ab)(cde)\circ (a...
by Xutar
Tue Mar 16, 2010 12:31 am UTC
Forum: Individual XKCD Comic Threads
Topic: 0714: "Porn For Women"
Replies: 298
Views: 67111

Re: "Porn For Women" Discussion

Does Randall not know what the phrase "Porn for ____" means?
Or if he does, is the only point of this comic pointing out that its meaning isn't sexual, as most internet porn is?
Either way, this comic seems pretty lame.
by Xutar
Sun Mar 14, 2010 4:20 pm UTC
Forum: Mathematics
Topic: Famous Math Quotes!
Replies: 32
Views: 8012

Famous Math Quotes!

It doesn't appear we have a thread for this yet, but I saw a few good ones in "Math Jokes" A few of my favorite are attributed to John von Neumann: "In mathematics you don't understand things. You just get used to them." and, "If people do not believe that mathematics is sim...
by Xutar
Sun Mar 07, 2010 11:14 pm UTC
Forum: Mathematics
Topic: Limit of a sum - I'm stuck.
Replies: 7
Views: 1751

Re: Limit of a sum - I'm stuck.

Have you gone over formal definition of an integral using a Riemann sum?
by Xutar
Mon Feb 22, 2010 2:09 pm UTC
Forum: Logic Puzzles
Topic: Puzzles from the xkcd book (big puzzle SOLVED!)
Replies: 147
Views: 161514

Re: Puzzles from the xkcd book

Are we sure part 3 (from page 1111, the crypto conference) is correct, and it is just the numbers on the screen? That and assumed part 4 bother me, since neither are directly labelled like the other parts. regarding part 3: Yes, the comic was also altered regarding the hair of the audience, which s...
by Xutar
Wed Feb 17, 2010 1:07 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 0703: "Honor Societies"
Replies: 234
Views: 59324

Re: Honor Societies

I just submitted my National Honors Society application 10 minutes ago (literally). Randall, stop-following-high-school-curricula-so-you-can-make-relevant-comics-to-your-high-school-target-audience my head!
by Xutar
Tue Feb 16, 2010 1:14 pm UTC
Forum: Mathematics
Topic: Favorite math jokes
Replies: 1452
Views: 489371

Re: Favorite math jokes

Henri Poincaré, once grew suspicious and started to weigh the bread loaves he was getting at the bakery. Indeed, he discovered that the average weight was 900 grammes (rather than 1 kg, as required). Accordingly, he reported the matter to the prefecture. A year later Poincare again visited the poli...
by Xutar
Wed Feb 10, 2010 9:23 pm UTC
Forum: Mathematics
Topic: today's blag problem
Replies: 23
Views: 3550

today's blag problem

This cool puzzle (and solution) comes from my friend Mike. Alice secretly picks two different real numbers by an unknown process and puts them in two (abstract) envelopes. Bob chooses one of the two envelopes randomly (with a fair coin toss), and shows you the number in that envelope. You must now ...
by Xutar
Wed Feb 03, 2010 1:06 pm UTC
Forum: Mathematics
Topic: Another implicit differentiation problem...
Replies: 4
Views: 773

Re: Another implicit differentiation problem...

What you had after "some simplification" is close, but I got this: y' = \frac{25x-4x^3-4xy^2}{4yx^2+4y^3+25y} Which doesn't simplify much further (you can put -x/y in the front and make it look more symmetric if you wish) You just dropped an x somewhere, these things happen edit: Sorry...
by Xutar
Tue Jan 19, 2010 8:15 pm UTC
Forum: Mathematics
Topic: Question on formulae for series
Replies: 4
Views: 608

Re: Question on formulae for series

Well what you wrote should have a summation i believe, and also \frac{}{} and \sum_{}^{} can be very useful
[imath]\sum_{r=1}^{n}r^2 = \frac{n(n+1)(2n+1)}{6}[/imath]

[imath]\sum_{r=1}^{n}r^3 = \frac{n^2(n+1)^2}{4}[/imath]
by Xutar
Thu Jan 14, 2010 7:16 pm UTC
Forum: Mathematics
Topic: RSA explanation
Replies: 23
Views: 2654

Re: RSA explanation

Im guessing he just wolfram'd it.
edit: im sure the wiki article on modular exponentiation can help
by Xutar
Sun Jan 10, 2010 5:28 am UTC
Forum: Mathematics
Topic: The "KGB" isn't all that ...
Replies: 27
Views: 3518

Re: The "KGB" isn't all that ...

whats a gogolplex?
by Xutar
Fri Jan 01, 2010 12:13 am UTC
Forum: School
Topic: Awesome Teacher Quotes
Replies: 1764
Views: 399893

Re: Awesome Teacher Quotes

My chem/bio teacher had this poster by her safety glasses cabinet:
Image
by Xutar
Mon Dec 28, 2009 6:12 am UTC
Forum: Logic Puzzles
Topic: Puzzles from the xkcd book (big puzzle SOLVED!)
Replies: 147
Views: 161514

Re: Puzzles from the xkcd book

regarding 101110 (the red and white block) We've already established that 207 factors into 9x23 which is the pixel dimensions of the block on 101110. However, you have to wonder if 1407 is actually relevant to this puzzle. After all, it is just the joke of the comic (2:07pm becoming 14:07 wh...
by Xutar
Thu Dec 17, 2009 12:24 pm UTC
Forum: Mathematics
Topic: Integration of e^( x^2)
Replies: 24
Views: 4215

Re: Integration of e^( x^2)

Hi everybody. I wanted to know if it was possible to integrate e^ (x^2) to get an exact function i. e not using the Taylor series... It is not possible to express the antiderivative of e^{x^{2}} in terms of elementary functions, but it is possible to find the exact value of some definite integrals ...
by Xutar
Mon Dec 14, 2009 2:48 am UTC
Forum: Forum Games
Topic: Maximize the post:views ratio! (if you look, you must post)
Replies: 36936
Views: 2427037

Re: Maximize the post:views ratio! (if you look, you must post)

oh damnit i accidently this thread again im not good with computer
by Xutar
Mon Dec 14, 2009 12:47 am UTC
Forum: Mathematics
Topic: Question on Monty Hall problem
Replies: 5
Views: 1139

Re: Question on Monty Hall problem

It seems to not change anything to me, except that now he can screw you over by picking the door with the car, then asking if you want to switch from a goat to another goat.
by Xutar
Sat Dec 12, 2009 9:54 pm UTC
Forum: Mathematics
Topic: Integration of e^( x^2)
Replies: 24
Views: 4215

Re: Integration of e^( x^2)

mikhail's definition isnt very useful because
[math]erf(x) = \frac{2}{\sqrt{\pi}}\int_0^x e^{-t^2} dt.[/math]
by Xutar
Fri Dec 11, 2009 12:54 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 0674: "Natural Parenting"
Replies: 100
Views: 23748

Re: "Natural Parenting" Discussion

Is it just me or does this comic also contain a terribad pun (besides the "mother of sampling bias" one)?
"Do what comes naturally"
by Xutar
Fri Nov 27, 2009 2:46 am UTC
Forum: General
Topic: Is your ZIP code prime?
Replies: 90
Views: 7584

Re: Is your ZIP code prime?

when i ran mine in my head i thought is was prime (44857) but then i checked with google, and apparently its 31*1447
by Xutar
Mon Oct 05, 2009 1:25 am UTC
Forum: General
Topic: what would you choose as your super power?
Replies: 636
Views: 73728

Re: Super-ish Powers

Very good coordination/reflexes/balance so I would never trip and would become an amazing dancer.
by Xutar
Sat Sep 19, 2009 4:35 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 0638: "The Search"
Replies: 139
Views: 35123

Re: "The Search" Discussion

am I the only one saying Scale fail here? It may be equivalent if the ants searched the entire earth, then concluded they were the only sentient life. Even that's less than how far weve reached out (on every conceivable electomagnetic spectrum too).
by Xutar
Wed Sep 09, 2009 2:15 pm UTC
Forum: Gaming
Topic: Guild Wars 2
Replies: 266
Views: 79621

Re: Guild Wars 2

Idk about that zergrush comment. Sway has become the dominant build among bad/inexperienced players. Anet is going to be nerfing the R/A dagger spammers soon though. Also, Anet announced they were going to eliminate Team arenas and Hero battes and add a new "sealed deck" arena; where you h...
by Xutar
Wed Sep 02, 2009 7:13 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 0631: "Anatomy Text"
Replies: 270
Views: 79438

Re: "Anatomy Text" Discussion

Just a quit warning to people hoping to check this. The top two results for "human genitals" on wikipedia are "Genital modification and mutilation" and "Genital Cutting".
by Xutar
Fri Aug 21, 2009 6:33 am UTC
Forum: Individual XKCD Comic Threads
Topic: 0626: "Newton and Leibniz"
Replies: 213
Views: 58739

Re: "Newton and Leibniz" Discussion

Well yes, but some could say Leibniz's contributions to calculus were..... INTEGRAL!
Spoiler:
YEEEEEEEEEEEEEEEEAAAAAAAAAAAAAAAAAAAAAAAAAH!
by Xutar
Wed Jul 15, 2009 7:18 pm UTC
Forum: Mathematics
Topic: Random Secretary problem
Replies: 5
Views: 1220

Re: Random Secretary problem

Thanks a lot, and yeah its possible I did I just wrote that out from memory.
by Xutar
Wed Jul 15, 2009 6:38 pm UTC
Forum: Mathematics
Topic: Random Secretary problem
Replies: 5
Views: 1220

Re: Random Secretary problem

well, yeah I suppose so, I guess it could be better worded as the probability is ~.623 for sufficiently large n.
by Xutar
Wed Jul 15, 2009 6:04 pm UTC
Forum: Mathematics
Topic: Random Secretary problem
Replies: 5
Views: 1220

Random Secretary problem

While reading through my entry-level Intro to Statistics textbook, this problem was outlined in a sidebar: Suppose a secretary has 50 letters and 50 addressed envelopes, but the letters get jumbled so that they are placed into the envelopes randomly. What is the probability that at least one envelop...
by Xutar
Wed Jul 15, 2009 5:46 pm UTC
Forum: Mathematics
Topic: Mathematics: Discovered or Invented?
Replies: 39
Views: 4782

Re: Mathematics: Discovered or Invented?

I voted invented. Obviously things like our decimal numbering system are crafted by us. Until you get heavily involved with quantum mechanical quations (i.e. "qubit" factoring computers) everything is derived from simple axioms (usually those of Peano Arithmetic). for example from addition...
by Xutar
Mon Jul 06, 2009 5:59 pm UTC
Forum: Science
Topic: What happens if you accelerate a neutron star?
Replies: 5
Views: 1815

Re: What happens if you accelerate a neutron star?

I believe "sparse" is the word you're looking for.
by Xutar
Sun Jun 28, 2009 2:21 am UTC
Forum: Mathematics
Topic: x^x = n, solving for x?
Replies: 18
Views: 2804

Re: x^x = n, solving for x?

if X^X equals N, then then N is exp(W(ln(N))) where W() denotes the Lambert W Function.

Edit: The Lambert W function is non-elementary, but the wiki page has some python code for computing a numeric value.
by Xutar
Thu Jun 25, 2009 12:11 am UTC
Forum: Science
Topic: How would you create a star?
Replies: 49
Views: 4494

Re: How would you create a star?

Is there some Godwin's law corollary that states as a science discussions length approaches infinity, the probability of a discussion on black holes occurring approaches 1?
by Xutar
Tue Jun 23, 2009 12:46 am UTC
Forum: General
Topic: Reset - In real life
Replies: 30
Views: 2779

Re: Reset - In real life

Actually, I think in the comic it was one of those paper-flipdown thingies. (where each day you flip to the next number on the right, then after 9, you flip to zero and move the left up one.)
by Xutar
Sun Jun 07, 2009 2:07 am UTC
Forum: Gaming
Topic: Plants Vs. Zombies
Replies: 51
Views: 9683

Re: Plants Vs. Zombies

Image
yes
by Xutar
Sat Jun 06, 2009 3:33 pm UTC
Forum: Mathematics
Topic: Why does the letter "b" represent the y-intercept?
Replies: 23
Views: 5811

Re: Why does the letter "b" represent the y-intercept?

I always though "m" stood for modulus? As in "The modulus of x; otherwise known as slope in 1st degree polynomials"
by Xutar
Tue Jun 02, 2009 8:23 pm UTC
Forum: Gaming
Topic: Guild Wars!
Replies: 58
Views: 3447

Re: Guild Wars!

I'm going to be honest that I don't play PvE hardly at all. If you ever get into PvP though, I could help you ascend from the ranks of nublet ASAP.
Don't let that discourage you from PMing me to ask for advice or w/e IGN: Klawron Crowcall
by Xutar
Tue Jun 02, 2009 11:33 am UTC
Forum: Mathematics
Topic: Why does the Limit of Sin(x)/x as x approaches 0 equal 1?
Replies: 37
Views: 11934

Re: Why does the Limit of Sin(x)/x as x approaches 0 equal 1?

This is similar to the statement:
lim x->0 (exp(x)-1)/x = exp(0) = 1
In that it is not intuitively algebraically or geometrically proovable. Its one of the fundamental pillars of calculus and limits in particular.
by Xutar
Tue Jun 02, 2009 11:30 am UTC
Forum: Mathematics
Topic: Strange bases
Replies: 14
Views: 2350

Re: Strange bases

There's a wiki article on complex bases . The most famous is the quater-imaginary base, which is basicaly quatanery with a radix of 2i (and much more common radix point notations, cause 1/i = -i). Also, base 1+i (or 1-i), which I dub "Biinary" is interesting because of its approximation of...
by Xutar
Mon Jun 01, 2009 7:45 pm UTC
Forum: Mathematics
Topic: Dreaming up mathematical principles.
Replies: 16
Views: 2496

Re: Dreaming up mathematical principles.

So basically, pi~3?
Shocking.

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