## Search found 17 matches

- Fri Oct 10, 2008 2:40 pm UTC
- Forum: Mathematics
- Topic: Tricky Counting Problem, any ideas?
- Replies:
**11** - Views:
**2397**

### Re: Tricky Counting Problem, any ideas?

How about finding the number of combinations in which some pair is next to each other, and subtracting from the total?

- Sun Sep 28, 2008 2:12 pm UTC
- Forum: Mathematics
- Topic: Naughty Functions
- Replies:
**59** - Views:
**6281**

### Re: Naughty Functions

OK, then, a non-negative continuous function that doesn't -> 0 but has finite integral as x -> infinity.

- Sat Sep 27, 2008 1:55 am UTC
- Forum: Mathematics
- Topic: Naughty Functions
- Replies:
**59** - Views:
**6281**

### Re: Naughty Functions

Right you are, and wrong I was!

- Fri Sep 26, 2008 3:40 pm UTC
- Forum: Mathematics
- Topic: Naughty Functions
- Replies:
**59** - Views:
**6281**

### Re: Naughty Functions

Based on my previous post, how about this (easy?) exercise: I described a function identically = 0 on an interval that then rises continuously at the interval's end. Now let's try smoothing it out at the corners. So... imagine any old function f and a real number a such that f(x) = 0 for x ≤ a f(x) ...

- Fri Sep 26, 2008 2:04 pm UTC
- Forum: Mathematics
- Topic: Naughty Functions
- Replies:
**59** - Views:
**6281**

### Re: Naughty Functions

How about a continuous function f with finite integral as x --> infinity but f(x) doesn't --> 0 as x -> infinity? An example would be f(x) = 0 everywhere except for intervals of length (1/2)^n centered on n. On those intervals, f rises to 1 and returns to 0 in series of ever-narrower triangular spik...

- Sat Sep 13, 2008 2:24 am UTC
- Forum: Mathematics
- Topic: Balls in balls in R^n
- Replies:
**25** - Views:
**4225**

### Re: Balls in balls in R^n

This problem is what professional mathematicians call, um, a ball-buster.

- Sat Aug 30, 2008 1:12 am UTC
- Forum: Mathematics
- Topic: Favorite mental math tricks/shortcuts
- Replies:
**61** - Views:
**10062**

### Re: Favorite mental math tricks/shortcuts

1. In doing everyday calculations, I try to treat everything as a common fraction. 15 is 3/2, 25 is 1/4, etc. Forget the decimal point and put it back at the end. Makes a lot of multiplication and division easier. 2. When computing discounted prices, use the distributive law. If something is 15% off...

- Tue Jul 22, 2008 1:36 am UTC
- Forum: Mathematics
- Topic: Differential Equations question
- Replies:
**8** - Views:
**1480**

### Re: Differential Equations question

And in the original equation was the square root also divided by x? I'm guessing not.

- Tue Jul 22, 2008 12:13 am UTC
- Forum: Mathematics
- Topic: Mathematicians on wikipedia display liberal bias
- Replies:
**35** - Views:
**6227**

### Re: Mathematicians on wikipedia display liberal bias

As Stephen Colbert once said, "Reality has a notorious liberal bias."

- Tue Jul 22, 2008 12:09 am UTC
- Forum: Mathematics
- Topic: Differential Equations question
- Replies:
**8** - Views:
**1480**

### Re: Differential Equations question

I don't follow your very first step. Maybe it's because you haven't included enough parentheses? If the original eqn is

[imath]xy' = (y/x) + [sqrt(x^2 + y^2)]/x[/imath]

then isn't

[imath]y' = y/x^2 + sqrt[(1/x^2) + (y/x^2)^2][/imath]

?

[imath]xy' = (y/x) + [sqrt(x^2 + y^2)]/x[/imath]

then isn't

[imath]y' = y/x^2 + sqrt[(1/x^2) + (y/x^2)^2][/imath]

?

- Fri Jul 11, 2008 3:00 am UTC
- Forum: Your art and links
- Topic: Raw Materials
- Replies:
**4** - Views:
**1876**

### Re: Raw Materials

Curious, to me, this trend toward comic strips where the art is getting more and more minimal and iconic. Even more curious to me is that I like 'em! 'Cause I was raised at a time when drawing was at least as important as writing in comics. What do it all mean?

- Fri Jul 11, 2008 2:45 am UTC
- Forum: Mathematics
- Topic: Question About the Pythagorean Theorem
- Replies:
**40** - Views:
**7769**

### Re: Question About the Pythagorean Theorem

The trig functions can be defined analytically, without reference to right triangles.

- Mon Jul 07, 2008 4:21 pm UTC
- Forum: Your art and links
- Topic: Raw Materials
- Replies:
**4** - Views:
**1876**

### Re: Raw Materials

keozen wrote:Love it, very cute

Cute... is that good? Yours is cute too--and good.

- Sat Jul 05, 2008 10:23 pm UTC
- Forum: Your art and links
- Topic: Raw Materials
- Replies:
**4** - Views:
**1876**

### Raw Materials

I'm a full-time cartoonist now, but I used to be a mathematician. Well, math grad student, really. Then a lot of my hair fell out. I just started a new web comic http://blogs.discovery.com/raw_materials/ that's tech-based. It may seem a bit, er, expressive compared to what we see here, but do let me...

- Sat Jul 05, 2008 10:12 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0443: "Know Your Vines"
- Replies:
**167** - Views:
**31876**

### Re: "Know Your Vines" Discussion

Um... what happened to your hands?

- Sun Jun 22, 2008 3:11 pm UTC
- Forum: Mathematics
- Topic: Favorite math jokes
- Replies:
**1452** - Views:
**494134**

### Re: Favorite math jokes

This may be lame, but I invented it myself:

Q. Why did the mathematical biologist get her nose pierced?

A. She wanted to change her genus.

Q. Why did the mathematical biologist get her nose pierced?

A. She wanted to change her genus.

- Sun Jun 22, 2008 2:57 pm UTC
- Forum: Mathematics
- Topic: Majoring in Math
- Replies:
**48** - Views:
**7935**

### Re: Majoring in Math

I say hang in there too, if you like math. The world needs mathematicians! I can tell you from my own experience that it's possible to convince yourself you're "not good enough" at just about any level of the game. Back in the Jurassic Period, I graduated Harvard w/ highest honors in math,...