# Quantum Mechanics Integral Trouble

1. Feb 28, 2008

### jakePHYS

1. Problem: int[(x^2)*(sin^2 (n*Pi*x/a)] from 0 to a

3. Physics teacher tells me to just look it up. I've wrestled with every table of integrals I can find (web, library, my books), but I'm still hung up.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 28, 2008

### Dick

Write it as x^2*sin(k*x) where k is n*pi/a. First use the trig identity sin^2(kx)=(1-cos(2kx))/2. Then to integrate something like x^2*cos(2kx) you just have to integrate by parts twice. It's not the easiest integral in the world, but it's not the hardest either.

3. Feb 28, 2008

### jakePHYS

Thnx

This has been vexing me for 3 1/2 weeks now! THANK YOU!

4. Feb 28, 2008