meta user
network profile
| bio | website | |
|---|---|---|
| location | Brooklyn, NY | |
| age | 31 | |
| visits | member for | 1 year, 8 months |
| seen | 2 days ago | |
| stats | profile views | 40 |
Good Morning how are you, I'm dr jimbob
I'm interested in things.
I'm not a real dr,
But I am a real jim bob.
Have a PhD in Experimental High-Energy Physics, but left academia in mid-2010 to program professionally.
Mostly program/script in python, django, and jquery these days doing mostly web apps.
Also have experience programming in C, C++, java, haskell, php, and (bash) shell more in the past.
Linux as primary OS since 1999, ubuntu user since 2005 (Hoary).
|
May 6 |
comment |
Prove $a+b+c+d $ is composite Note this does not work if you include 0 in the natural numbers. (Obvious counterexample: a = 0, b=3, c=0, d=4, so ab = cd = 0, but a+b+c+d=7 which is prime). |
|
Feb 11 |
answered | 2013th derivative of a trigonometric function |
|
Jan 11 |
revised |
How to make two vectors orthogonal? added 227 characters in body |
|
Jan 11 |
revised |
How to make two vectors orthogonal? Very sloppy bad math on my part. |
|
Jan 11 |
revised |
How to make two vectors orthogonal? added 112 characters in body |
|
Jan 11 |
answered | How to make two vectors orthogonal? |
|
Jan 11 |
comment |
How to make two vectors orthogonal? It's not Gramm-Schmidt. It's Gram-Schmidt (assuming you want to take a set of vectors that spans some space and create a new set of orthogonal vectors - typically also normalized - that spans the same space). |
|
Jan 10 |
comment |
How to solve this calculus problem? @MaoYiyi - There an infinite number of potential functions $f(x)$ that satisfy the given property (e.g., if you assume a form of Ax^4 + Bx^3 + Cx^2 + Dx + E; then A=-134/2475, B = 3622/2475, C=-31924/2475, D=106937/2475, E= -7369/165; or you could assume Ax^10+Bx^8+Cx^6+Dx^4+Ex^2 and get a totally different answer that meets the criteria). E.g., you can give a rough estimate of f'(2.5) based on f(2), f(3) -- even if its more of an average value of f'(x) between 2 and 3. |
|
Jan 10 |
comment |
How to solve this calculus problem? @proximal - I was trying to not suggest evaluate the limit, but to see f'(x) = lim h->0 (f(x+h) - f(x-h))/(2h) we can approximate f'(x) ~ (f(x+h) - f(x-h))/(2h) at several points, exactly as you said. Just was trying to leave it as "hints". |
|
Jan 10 |
answered | How to solve this calculus problem? |
|
Dec 11 |
comment |
Does multiplying polynomials ever decrease the number of terms? Generalizing; let a,b,c,d be non-zero. (x^2 + a x + b)(x^2 + c x + d) = x^4 + (a+c)x^3 + (ac+b+d )x^2 + (ad + bc) + b d. So if a+c = 0, ad + bc + 0, and ac + b+ d = 0 it works. The first eqn gives c = -a; which reduces the second equation to (a)(d-b) = 0, and since a is non-zero means b=d. Hence the last equation becomes 2b - a^2 = 0. So this works for any non-zero a of the form: (x^2 + a x + a^2/2)(x^2 - ax + a^2/2). |
|
Nov 9 |
comment |
List of interesting integrals for early calculus students This is a great integral to show; but not for his purpose without students being exposed to multi-d calculus or being given many hints. |
|
Nov 9 |
revised |
List of interesting integrals for early calculus students Add missing negative sign. |
|
Aug 31 |
awarded | Yearling |
|
Jul 31 |
comment |
Solving $5^n > 4,000,000$ without a calculator @Polynomial - Can you easily solve that without a calculator? I get to 5^(n-308) > 2^312*3*13 or so and then need to estimate log(2)/log(5) part to enough precision that I can multiply by a three digit number and know I'm not off by 1 or introduce approximations 624 ~ 625. I can sort of estimate values (e.g., Newton's method) to get within about ~1 (I find N=444 instead of 445), but would be very hard to prove. |
|
Jul 23 |
answered | Proof of the divisibility rule of 17. |
|
Jul 14 |
awarded | Good Answer |
|
Apr 29 |
awarded | Commentator |
|
Apr 29 |
comment |
How to avoid arithmetic mistakes? @DHall - It still works, because 5+6+7=18 and 18 ≡ 0 mod 9, and 0 x 3 = 0 and 9 ≡ 0 mod 9. You should recognize that casting out nines will silently work with an arithmetic mistake 1/9 times. |
|
Mar 8 |
answered | Coin sequence paradox from Martin Gardner's book |
