Question

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

Answer 1

`f'(x) = cosx`

Explanation:

This is a trick or trap question.

The long and tedious way to this in by the product rule, then simplify.

The quicker way is to observe that

`f(x) = tanx cosx = sinx/cosx cosx = sinx`.

So, `f'(x) = cosx`.