Question

What is the derivative of `f(x)=secxcosx`?

Answer 1

`f'(x)=0` for all `x != pi/2+pik` (`k` an integer.)

Explanation:

For all `x` in the domain of `secx`, we have

`f(x) = secx cosx = 1/cosx cosx = 1`.

So `f'(x) = 0`