Question

What is the derivative of `y=(cosx)(tanx)`?

Answer 1

It is `cosx`

You could use the product rule and simplify later, but I think it's easier to simplify first: `tanx = sinx/cosx`, so this `y` simplifies to :

`y=cosx tanx = cosx sinx/cosx=sinx`

So `y' = cosx`