# What is the second derivative of f(x)=cos(-x)-sinx?

Jan 14, 2016

$f ' ' \left(x\right) = - \cos x + \sin x$

#### Explanation:

The function can be simplified as

$f \left(x\right) = \cos x - \sin x$

Differentiating once:

$f ' \left(x\right) = - \sin x - \cos x$

Differentiating again:

$f ' ' \left(x\right) = - \cos x + \sin x$