I don't even know where to start with this:

d/dx f(sin(x))=1/(cos(x))

find a formula for f'(x)

This is a review question and I've tried expanding f'(sin(x)) but nothing

I just need a hint to how I get started on this problem

Oh I know the answer to f'(x) is 1/(1-x^2) but I got it from trial and error is there a mathematical way