Power-Reduction Identities

Identity Type Formula
Sine \[ \sin^2 x = \frac{1 - \cos 2x}{2} \]
Cosine \[ \cos^2 x = \frac{1 + \cos 2x}{2} \]
Tangent \[ \tan^2 x = \frac{1 - \cos 2x}{1 + \cos 2x} \]