Derivative of Inverse Trigonometric Functions

f(x) = cos(arcsin(2x))

What is f'(x)?

4 answers

I did this down below, after the one drwls answered
copied:

It is so similar that you should be able to do it the same way. Draw the triangle and you have sqrt(1-4x^2)
f(x) = (1-4x^2)^.5
f'(x) = .5 [(1-4x^2)^-.5] (-8x)
= -4x/sqrt(1-4x^2)
Oh.

But the text book I'm using gives me the answer:

Sqrt(1-4x^2)

No denominators or anything.
That is just the first step.