## Search found 209 matches

- Thu Feb 21, 2008 11:52 pm UTC
- Forum: Mathematics
- Topic: Sin(q*pi)=r; q,r rational
- Replies:
**7** - Views:
**1866**

### Sin(q*pi)=r; q,r rational

I got started on this problem while traveling down on a tangent to my algebra homework. Let Q be the rationals and R be the reals. Define f:Q->R by f(q)=Cos(q*pi). How many elements are in f(Q) \cap Q? (by \cap I mean intersect). edit: Yes I did mean "f(Q) \cap Q" and not "f(Q) \cap R...

- Thu Jan 24, 2008 2:12 am UTC
- Forum: Mathematics
- Topic: Calculating Frenet triples in mathematica
- Replies:
**2** - Views:
**1228**

### Calculating Frenet triples in mathematica

Does anyone know if mathematica can calculate the curvature and torsion of a vector function? I would like to double check my geometry homework.

- Thu Jan 10, 2008 5:39 pm UTC
- Forum: Mathematics
- Topic: Math bloopers heard in math classes
- Replies:
**252** - Views:
**35261**

### Re: Math bloopers heard in math classes

The worst math teacher I ever had (first day of class):a meter is a different length in the evening then it is in the morning Me:*headache* Teacher:this is because in the evening the meter stick is warmer, and expands slightly. Me:<explanation of how the meter is defined as the distance light goes ...

- Wed Jan 09, 2008 2:11 am UTC
- Forum: Language/Linguistics
- Topic: Whence and hence
- Replies:
**19** - Views:
**6744**

### Re: Whence and hence

OK, I think I've got it. If you make statement P and wish to smoothly statement Q, an implication of P, then you use "whence". Example: "All prime numbers greater than 2 are odd, whence 22 is not prime." Hence on the other hand is used to start a statement, and if I wished to emp...

- Mon Jan 07, 2008 7:20 pm UTC
- Forum: Language/Linguistics
- Topic: Whence and hence
- Replies:
**19** - Views:
**6744**

### Whence and hence

My algebra teacher uses whence a lot where I would have expected him to use hence. He is always mentioning word histories as new words get brought up in lectures and in his speech it is obvious that he tries consciously to use a very precise vocabulary, so I can only assume he picks whence over henc...

- Wed Jan 02, 2008 8:33 pm UTC
- Forum: Mathematics
- Topic: Division by Zero (Please, no new threads about this)
- Replies:
**367** - Views:
**84432**

### Re: Division by Zero (Please, no new threads about this)

Why so much hate? Learning what is not true is just as important as learning what is true.

Isn't the completion of Q unique?

After all, Q is our general field, R is just one of many completions. Shouldn't this be discussed(if at all) in Q?

Isn't the completion of Q unique?

- Sun Dec 30, 2007 10:44 pm UTC
- Forum: Mathematics
- Topic: Urysohn lemma
- Replies:
**5** - Views:
**1475**

### Re: Urysohn lemma

Maybe I just didn't get the obviousness of the rest of the proofs in my topology course, so this one didn't seem like it was on a totally different level. That course kicked my ass. Although my teacher kept telling us that the the proofs were all trivial and the definitions made the class hard. Mayb...

- Sun Dec 30, 2007 10:02 pm UTC
- Forum: Mathematics
- Topic: Urysohn lemma
- Replies:
**5** - Views:
**1475**

### Urysohn lemma

In my topology book by Munkres, the Urysohn lemma is described as "the first deep theorem of the book" because its proof involves a very original idea that very very few people could come up with on their own. I am a little self conscious on my basic proof skills and I feel like it is some...

- Sun Dec 30, 2007 12:37 am UTC
- Forum: Mathematics
- Topic: Division by Zero (Please, no new threads about this)
- Replies:
**367** - Views:
**84432**

### Re: 0/0 = {R} U {I} ?

No, sorry but you are not correct. First off its not "undefined" its "indeterminate" Say 0*x=0 therefore 0/0=x if it wasn't indeterminate. But isn't there another number a not equal to x such that 0*a=0 therefore a=x, which is a contradiction. Also, x/0=undefined and 0/x = 0 if ...

- Sat Dec 15, 2007 5:34 am UTC
- Forum: Mathematics
- Topic: Favorite math jokes
- Replies:
**1452** - Views:
**489192**

### Re: Favorite math jokes

Ended wrote:(from here)

Q: Do you know any catchy anagram of Banach-Tarski?

A: Banach-Tarski Banach-Tarski

- Mon Dec 10, 2007 2:54 am UTC
- Forum: Mathematics
- Topic: Amusing answers to tests
- Replies:
**393** - Views:
**60698**

### Re: Amusing answers to tests

A friend's answer for the chemistry exam the week before last. The question was something along the lines of You are a hydrogen molecule in a balloon filled with equal moles of hydrogen and oxygen molecules at 2 atm pressure. A student ignites the balloon with a match. Describe: 1) What you see ini...

- Sun Dec 02, 2007 1:47 am UTC
- Forum: Mathematics
- Topic: Favourite Field of Math?
- Replies:
**60** - Views:
**5394**

### Re: Favourite Field of Math?

This has been my experience so far: in Calculus you learn how to calculate things (like derivatives, integrals, areas, volumes, limits, etc.); whereas in Analysis, you learn how to prove things. I guess you could say the difference is in rigor. Or else you could say one is learning how to use the to...

- Thu Nov 29, 2007 9:51 pm UTC
- Forum: Mathematics
- Topic: What proofs are (split from amusing test answers)
- Replies:
**37** - Views:
**3943**

### Re: What proofs are (split from amusing test answers)

I think the question is not "Are the logical rules of inference true?". Nor is it "Are these postulates true?". But rather "Do these rules model how we think well?" and "Are these postulates good models for our intuitive idea of the object at hand?" I don't th...

- Fri Nov 23, 2007 6:29 am UTC
- Forum: Mathematics
- Topic: Favourite Erroneous "Proofs"
- Replies:
**194** - Views:
**43444**

### Re: Favourite Erroneous "Proofs"

If a relation is symmetric and transitive, then it is also reflexive. (I came up with this one myself during a lecture today, I was quite proud) a R b, b R c -> a R c that is transitivity. let c=a. a R b, b R a -> a R a since the first half of that proposition is true for a symmetric R , we can be ...

- Thu Nov 22, 2007 8:32 pm UTC
- Forum: Mathematics
- Topic: Uh oh. My math teacher says .999... does not equal 1.
- Replies:
**9** - Views:
**3945**

### Re: Uh oh. My math teacher says .999... does not equal 1.

Yeah, IVT has to do with functions... what function was even mentioned??

What the teacher is incorrectly trying to apply is the fact that the real numbers are dense. That is, every number in the set of the real numbers is a limit point.

What the teacher is incorrectly trying to apply is the fact that the real numbers are dense. That is, every number in the set of the real numbers is a limit point.

- Wed Nov 21, 2007 8:29 am UTC
- Forum: Mathematics
- Topic: Fluency with mathematical proofs.
- Replies:
**18** - Views:
**3068**

### Re: Fluency with mathematical proofs.

I second the buying your intro to abstract math book early. I read (here I think - there is an older thread about reading proofs that I couldn't find after a quick search) that papers written by John Conway are good for beginners because they are easy to understand. Haven't checked his stuff out bey...

- Mon Nov 19, 2007 12:33 am UTC
- Forum: Mathematics
- Topic: sylow subgroups
- Replies:
**15** - Views:
**2510**

### Re: sylow subgroups

if q

^{x}is not congruent to 1 mod p, for all 0<x<b- Sun Nov 18, 2007 6:40 am UTC
- Forum: Mathematics
- Topic: Amusing answers to tests
- Replies:
**393** - Views:
**60698**

### Re: Amusing answers to tests

Once my friend and I turned in our weekly notebook photocopies for our electical engineering class late. As a way of reconciling with the TA, I put a $5 bill on the title page, but I did it pre-photocopy.

Yeah, it was funnier at the time...

Yeah, it was funnier at the time...

- Sat Nov 17, 2007 4:10 am UTC
- Forum: Mathematics
- Topic: sylow subgroups
- Replies:
**15** - Views:
**2510**

### Re: sylow subgroups

btilly - nice. I guess I don't see how (3456) generates the other cycles though. I haven't slept in a while.

Guess: is it because of the inverses? I don't have a solid understanding of what inverses look like yet.

Guess: is it because of the inverses? I don't have a solid understanding of what inverses look like yet.

- Fri Nov 16, 2007 11:43 pm UTC
- Forum: Mathematics
- Topic: Fast-tracking mathematics.
- Replies:
**55** - Views:
**4758**

### Re: Fast-tracking mathematics.

All I have to offer is advice: There is no substitute for treadging through the boring classes. You might be able to pick up the ideas and the basics, and even pass any test that you would have to pass in the boring classes, but it's not the same. If you want to go far in a subject (and I guess this...

- Fri Nov 16, 2007 11:33 pm UTC
- Forum: Mathematics
- Topic: sylow subgroups
- Replies:
**15** - Views:
**2510**

### sylow subgroups

Just had my algebra midterm, things went well, except I couldn't figure this one out: Find a 2-Sylow subgroup of the symmetric group on 6 letters, S 6 . I had no idea how to approach this, so with nothing to lose that I wouldn't lose anyway by leaving the answer blank, I started with (14), (25), (36...

- Tue Nov 13, 2007 12:24 am UTC
- Forum: Mathematics
- Topic: Proficiency with LaTeX
- Replies:
**86** - Views:
**14147**

### Re: Proficiency with LaTeX

How do you write out a multi-part function?

- Sat Nov 10, 2007 7:50 am UTC
- Forum: Mathematics
- Topic: On Linear Algebra
- Replies:
**35** - Views:
**4224**

### Re: On Linear Algebra

For everyone who says you don't need any calculus to do linear algebra, have you ever heard of the wronskian? Not only did I cover it in my linear algebra class, but the students I tutor are learning it, at a separate university, in their linear algebra class. Admittedly it's not that major of a top...

- Thu Nov 08, 2007 4:35 pm UTC
- Forum: Mathematics
- Topic: Proof by contradiction is never needed!
- Replies:
**22** - Views:
**2822**

### Re: Proof by contradiction is never needed!

What about the proof that sqrt(2) is irrational? The direct statement would presumably be: (x^2 = 2) => (x is irrational) So the contrapositive would be that: (x is rational) => (x^2 =/= 2) This doesn't seem (to me) easy to do without contradiction somewhere. x=n/d => n^2 has an even number of 2s i...

- Tue Nov 06, 2007 7:47 pm UTC
- Forum: Mathematics
- Topic: series and limsups
- Replies:
**1** - Views:
**845**

### series and limsups

The official ratio and root tests use the limsup of a n and not just the lim. On the other hand if lim a n converges, then limsup=liminf=lim. But then if a series converges, then lim a n must not only converge, but converge to 0. So, why limsup? ... OK, actually I just realized while typing this tha...

- Thu Nov 01, 2007 4:58 am UTC
- Forum: Mathematics
- Topic: Inverting Laplace Transforms
- Replies:
**6** - Views:
**1539**

### Re: Inverting Laplace Transforms

All I know is that laplace transforms kicked ass when I was analyzing circuits. I vaguely remember that multiplication in the laplace domain was addition in the time domain. So the inverse of F(s) would work out to be

L

L

^{-1}(e^{-2s})+L^{-1}(2/s^{2}-4)- Sat Oct 27, 2007 4:45 am UTC
- Forum: Mathematics
- Topic: Ways of making a team
- Replies:
**3** - Views:
**1112**

### Re: Ways of making a team

One way to do it is:

5C4 + (5C3*5C1) + (5C2*5C2) + (5C1*5C3)

where aCb is "a choose b" or a!/[(a-b)!*b!]. So it's:

5!/4! + 2*5!*5!/(4!*2!*3!) + [5!/(3!*2!)]^2

5 + 14400/144 + (120/12)^2

5 + 100 + 100

= 205

What is your method trying to do? Where did your numbers come from?

5C4 + (5C3*5C1) + (5C2*5C2) + (5C1*5C3)

where aCb is "a choose b" or a!/[(a-b)!*b!]. So it's:

5!/4! + 2*5!*5!/(4!*2!*3!) + [5!/(3!*2!)]^2

5 + 14400/144 + (120/12)^2

5 + 100 + 100

= 205

What is your method trying to do? Where did your numbers come from?

- Fri Oct 26, 2007 4:24 am UTC
- Forum: Mathematics
- Topic: cantor set = set of all what in base 3?
- Replies:
**3** - Views:
**1220**

### cantor set = set of all what in base 3?

Reading through my notes in my Real Analysis class, I wrote down that the cantor set P = {x \in \R | x has n 1s in its base three expansion}. I guess I forgot to put what n was. Is n any element of Z? Did I mean to write 'inf'? Little help please?

- Thu Oct 25, 2007 7:23 pm UTC
- Forum: Mathematics
- Topic: Halp at Toplogy!
- Replies:
**10** - Views:
**1431**

### Re: Halp at Toplogy!

I see what you are saying, and I think the last two questions are indeed equivalent. Yes, you cannot take the union of all the elements of a basis without covering S. OK wait stop. One of the possibly confusing points of topology is that a topological space consists of TWO sets. Here I am going to u...

- Thu Oct 25, 2007 4:45 am UTC
- Forum: Mathematics
- Topic: Halp at Toplogy!
- Replies:
**10** - Views:
**1431**

### Re: Halp at Toplogy!

But that is the usual definition, n'est pas? Nope. First of all, in the usual definition, the basis has to cover S, not just be able to create all open sets by union. This is a necessary condition for S to be made up of a union of elements of the basis. If the basis did not cover S, then arbitrary ...

- Thu Oct 25, 2007 12:50 am UTC
- Forum: Mathematics
- Topic: Math movies
- Replies:
**34** - Views:
**3931**

### Re: Math movies

23 was awesome I thought. It gave me nightmares

edit: "The Number 23" I guess

edit: "The Number 23" I guess

- Mon Oct 22, 2007 11:52 pm UTC
- Forum: Mathematics
- Topic: Spanish help
- Replies:
**14** - Views:
**2524**

### Re: Spanish help

Topology -> topología Set -> conjunto Complex number -> número complejo field -> campo metric space -> espacio métrico theorem -> teorema prove -> demostrar proof -> demostración element -> elemento region -> región La próxima vez vete a un foro hispanohablante ;-) [next time go to a spanish-speaki...

- Sun Oct 21, 2007 9:40 pm UTC
- Forum: Mathematics
- Topic: Spanish help
- Replies:
**14** - Views:
**2524**

### Re: Spanish help

Did you try what I said in my PM? Yeah, so the suggestion was to look it up in wikipedia then change the language for that article to spanish. To be honest, I haven't tried it yet, but it sounds like a good idea. ... OK I just tried it, and since the axiom of choice wasn't in any of the other place...

- Sun Oct 21, 2007 5:47 pm UTC
- Forum: Mathematics
- Topic: Proficiency with LaTeX
- Replies:
**86** - Views:
**14147**

### Re: Proficiency with LaTeX

Has anyone found a nice way to title homework assignments? I kind of want to use \maketitle, just because it's there and it makes so much sense, but is there a way of toning it down a little so it fits more the style of "just another assignment"? Use the report document type? Even worse -...

- Sun Oct 21, 2007 4:37 am UTC
- Forum: Mathematics
- Topic: Proficiency with LaTeX
- Replies:
**86** - Views:
**14147**

### Re: Proficiency with LaTeX

Has anyone found a nice way to title homework assignments? I kind of want to use \maketitle, just because it's there and it makes so much sense, but is there a way of toning it down a little so it fits more the style of "just another assignment"?

- Sat Oct 20, 2007 11:59 pm UTC
- Forum: Mathematics
- Topic: Proficiency with LaTeX
- Replies:
**86** - Views:
**14147**

### Re: Proficiency with LaTeX

Does anyone know how to apply a condition underneath a large union? For instance the union of B_{alpha} over a collection alpha. Like this http://upload.wikimedia.org/math/1/4/f/14ff2c1ffddc8472a030c5ad6f6ebc5f.png ? If so then \bigcap_{\alpha \in A} B_\alpha Thanks! It seems like it only works in ...

- Sat Oct 20, 2007 10:28 pm UTC
- Forum: Mathematics
- Topic: Proficiency with LaTeX
- Replies:
**86** - Views:
**14147**

### Re: Proficiency with LaTeX

Does anyone know how to apply a condition underneath a large union? For instance the union of B_{alpha} over a collection alpha.

- Sat Oct 20, 2007 5:43 am UTC
- Forum: Mathematics
- Topic: Spanish help
- Replies:
**14** - Views:
**2524**

### Spanish help

Como se dicen las siguientes frases en espanol?

Topology

Set

Complex number

field

metric space

theorem

prove

proof

element

region

En cambio, hay algun sitio donde se puede buscar las palabras de las matematicas?

Topology

Set

Complex number

field

metric space

theorem

prove

proof

element

region

En cambio, hay algun sitio donde se puede buscar las palabras de las matematicas?

- Tue Oct 16, 2007 6:01 pm UTC
- Forum: Mathematics
- Topic: Are there jordan curves with non-zero area?
- Replies:
**15** - Views:
**5512**

### Re: Are there jordan curves with non-zero area?

http://img146.imageshack.us/img146/6720/96p00523l1ad3.th.gif http://img266.imageshack.us/img266/8526/96p00523l2ws2.th.gif http://img266.imageshack.us/img266/9136/96p00523l4lf0.th.gif http://img266.imageshack.us/img266/4773/96p00523l5kr6.th.gif http://img152.imageshack.us/img152/5084/96p00523l7ij7.t...

- Tue Oct 16, 2007 7:46 am UTC
- Forum: Mathematics
- Topic: Are there jordan curves with non-zero area?
- Replies:
**15** - Views:
**5512**

### Re: Are there jordan curves with non-zero area?

Apparently the answer is yes:

http://links.jstor.org/sici?sici=0002-9947(190301)4%3A1%3C107%3AAJCOPA%3E2.0.CO%3B2-T

http://links.jstor.org/sici?sici=0002-9947(190301)4%3A1%3C107%3AAJCOPA%3E2.0.CO%3B2-T