Double Angle Formula for Cosine/Corollary 5

Corollary to Double Angle Formula for Cosine

 * $1 - \cos \theta = 2 \sin^2 \dfrac \theta 2$

Proof
From Double Angle Formula for Cosine: Corollary 2:
 * $\cos 2 \theta = 1 - 2 \sin^2 \theta$

The result follows from substituting $\dfrac \theta 2$ for $\theta$ and rearranging.