Thread: Integration by trig substitutions.

Edit: stupid mistake. I didn't have anything wrong to begin with.

Just substitute $\displaystyle x = 3\sin{\theta}$

then $\displaystyle dx = 3\cos{\theta}d\theta$

You should end up at $\displaystyle \int \cot^2{\theta} d\theta$

That's... exactly where I am now. My substitutions were different than yours, but they give the same exact problem.