If you're going to use a trig substitution, then subbing would fit.
A neater approach would be to sub
I am struggling with the integral dx/(x^2*sqrt(16x^2-9)). I know the bottom can be broken down using trig substitution to get to x^2*tan^2(theta) but then I get stuck. Any hints on where to go next? Or am I looking at this problem in the wrong direction? Thanks.