Question

What is the derivative of `ln(cos^2(x))`?

Answer 1

`f(x) = ln(cos^2x) = ln((cosx)^2) = 2ln(cosx)`

Explanation:

`f'(x) = 2 1/cosx (-sinx)` `" "` (Chain rule: `d/dx(lnu) = 1/u (du)/dx`)

`= -2tanx`