# Homework Help: Help with trigonometric substitution

1. Feb 22, 2013

### ronybhai

1. The problem statement, all variables and given/known data

integral (1)/(x^2sqrt(36-x^2)

2. Relevant equations

3. The attempt at a solution
I found X=6sinθ dx=6cos
√(36-x^2)=√(36-sin^2θ)=6cosθ
i think the problem is that i am not getting integral of ∫csc^2θ

2. Feb 22, 2013

### Dick

You should. Show the rest of your work so someone can tell you where you went wrong.

3. Feb 22, 2013

### ronybhai

i know the answer which is -√(36-x^2)/36x+C

4. Feb 22, 2013

### Dick

That's not the rest of your work, that's what I asked for. You've got a cos(θ) and the numerator and cos(θ) in the denominator. They cancel. What's left?

5. Feb 22, 2013

### KDeep

The integral is -cotθ + C

6. Feb 22, 2013

### Dick

That's part of it. There's also a constant around. But like we were talking about in your last post there is a way to express -cot(arcsin(x/6)) as a function of x without any trig functions. That's what the books answer is.