# Integration by substitution question

1. Apr 22, 2003

### Einstein

How do you do this question, Ive spent hours figuring it out:

Use the substitution x = 3sint to show that

3
[inte]x^2[squ](9-x^2) dx = (81/16)pi
0

2. Apr 22, 2003

### Mulder

Have you got it anywhere near [inte] 81 (sint)^2 * (cost)^2 dt from 0 to [pi]/2 yet? You can make a substitution from there. If you haven't, have you forgot to substitute dx for 3cost dt, and changed the limits?

3. Apr 22, 2003