# $\cos{(A+B)}$ formula

## Formula

$\cos{(A+B)}$ $\,=\,$ $\cos{A}\cos{B}$ $-$ $\sin{A}\sin{B}$

### Introduction

$A$ and $B$ are two angles, whose sum is $A+B$. Cosine of sum of angles $A$ and $B$ is written as $\cos{(A+B)}$ in trigonometric mathematics. The $\cos{(A+B)}$ identity is used as a formula in trigonometry and used to expand in terms of cos and sin of angles $A$ and $B$.

#### Proof

Learn how to derive cos of sum of angles in geometrical method.