Geometry & Trigonometry
Intermediate

Cosine Angle Sum

Angle addition formula for cosine.

Formula

cos⁡(A±B)=cos⁡Acos⁡B∓sin⁡Asin⁡B\cos(A \pm B) = \cos A\cos B \mp \sin A\sin B

Variables

A, BAngles

Example

cos 75° = cos(45°+30°) = cos45cos30 − sin45sin30 ≈ 0.259.

Did You Know?

These sum formulas let you compute the sine or cosine of an angle by breaking it into known pieces.

trigonometryidentitysum