Trigonometry
Intermediate

Double Angle: Cosine

Cosine of twice an angle (also 2cos²θ−1 or 1−2sin²θ).

Formula

cos⁡2θ=cos⁡2θ−sin⁡2θ\cos 2\theta = \cos^2\theta - \sin^2\theta

Variables

\thetaAngle

Did You Know?

Three equivalent forms of the cosine double-angle formula exist, each handy for a different simplification.

double angleidentity