# What is the derivative of sin(x + (π/2)) ?

May 5, 2018

The derivative is $- \sin x$.

#### Explanation:

Rewrite using the sum rule:

$= \sin x \cos \left(\frac{\pi}{2}\right) + \cos x \sin \left(\frac{\pi}{2}\right)$

$= \cos x$

We know from basic differentiation rules that $\frac{d}{\mathrm{dx}} \left(\cos x\right) = - \sin x$.

Hopefully this helps!