Question

What is the derivative of `f(x)=2cosx-cos2xdx`?

Answer 1

`-2sin x+2sin 2x`

Explanation:

Note that

`d/(dx)(2cos x - cos 2x)= 2d/(dx)(cosx )-d/(dx)(cos 2x)`
`=-2sin x+2sin 2x`

Since `d/(dx)(cos x) = -sin x` and `d/(dx)(cos2x)= -2sin2x`.