## Search found 11 matches

- Tue Dec 08, 2009 9:44 pm UTC
- Forum: Mathematics
- Topic: Matrices and how they transform graphs
- Replies:
**28** - Views:
**2875**

### Re: Matrices and how they transform graphs

you're right, matrix multiplication is in general not commutative (order matters). reflecting then rotating gives something different to rotating then reflecting. a minor point, AS=SA for all A iff S is a scalar multiple of the identity matrix. You might like to try proving this yourself, it's not ...

- Tue Dec 08, 2009 9:40 pm UTC
- Forum: Mathematics
- Topic: Matrices and how they transform graphs
- Replies:
**28** - Views:
**2875**

### Re: Matrices and how they transform graphs

Scalar multiple as in a*I where a is a scalar and I is the identity matrix. so, for example a matrix with all 5's on the diagonal and nothing else

- Tue Dec 08, 2009 8:56 am UTC
- Forum: Mathematics
- Topic: Matrices and how they transform graphs
- Replies:
**28** - Views:
**2875**

### Re: Matrices and how they transform graphs

you're right, matrix multiplication is in general not commutative (order matters). reflecting then rotating gives something different to rotating then reflecting. a minor point, AS=SA for all A if and only if S is a scalar multiple of the identity matrix. You might like to try proving this yourself,...

- Thu Nov 12, 2009 5:47 am UTC
- Forum: Mathematics
- Topic: Simple Factoring...
- Replies:
**7** - Views:
**1084**

### Re: Simple Factoring...

a short way to do the second:

x^4 + 8x^2 + 144 = (x^2+12)^2 - 16x^2 = (x^2+12-4x)(x^2+12+4x)

the last step is difference of 2 squares.

x^4 + 8x^2 + 144 = (x^2+12)^2 - 16x^2 = (x^2+12-4x)(x^2+12+4x)

the last step is difference of 2 squares.

- Wed Nov 11, 2009 6:43 am UTC
- Forum: Mathematics
- Topic: Ten Problems for Geometrical Intuition
- Replies:
**58** - Views:
**5827**

### Re: Ten Problems for Geometrical Intuition

re q4 see pic: http://img23.imageshack.us/img23/9899/circlel.jpg Note that sliding the stick around is equivalent to moving the point on the circumference around. (remember that high school theorem, any triangle in a circle with diameter as one side and the other point on the circumference is a ...

- Thu Oct 29, 2009 11:21 am UTC
- Forum: Mathematics
- Topic: Apparently easy complex number problem
- Replies:
**20** - Views:
**2136**

### Re: Apparently easy complex number problem

just let z / (z - i) = r where r is real, then solve for z.

- Tue Oct 13, 2009 9:34 am UTC
- Forum: Mathematics
- Topic: Becoming a Mathematician?
- Replies:
**17** - Views:
**4676**

### Re: Becoming a Mathematician?

"If nothing else, universities around the world (but particularly under the US system) need huge numbers of people to teach maths to undergrads, and not just those undergrads specialising in maths either."

isn't that what phds students and postdocs are for though?

isn't that what phds students and postdocs are for though?

- Wed Oct 07, 2009 12:59 pm UTC
- Forum: Mathematics
- Topic: Expression that alternates between 0 and 1?
- Replies:
**13** - Views:
**5081**

### Re: Expression that alternates between 0 and 1?

i'm curious, what was the question?

- Wed Aug 05, 2009 12:55 pm UTC
- Forum: Mathematics
- Topic: Book Club: Mathematics: Its Contents... discussion
- Replies:
**50** - Views:
**5349**

### Re: Book Club: Mathematics: It's Contents... discussion

you guys might find mathim.com useful. real time chat + latex, no rego required. bit laggy though.

- Sat May 02, 2009 5:30 am UTC
- Forum: General
- Topic: Who the dickens are you?
- Replies:
**10922** - Views:
**2381305**

### Re: INTRO THREAD THE THIRD

hi, my name is Bobo, 17/male/melbourne ive been into maths and programming since about 15, other recent interests include unicyling and playing recorder i'm in my first year of science/mechanical engineering at monash uni, but i'm starting to have second thoughts about the engineering part. proving ...

- Sun Sep 14, 2008 10:47 am UTC
- Forum: Coding
- Topic: Project Euler
- Replies:
**411** - Views:
**158714**

### Re: Project Euler

why is my sieve so slow? the one above me takes 0.0940001010895 seconds to run, for n = 100,000 whereas mine takes 85.8440001011: import time def prsieve(N): 'Returns all primes <= N in list prim' prim = [] prim = range(2,N+1) n = 0 p = 0 while p <= N**.5: p = prim[n] for x in prim: if x%p == 0 and ...