Double Angle Formula for Cosine/Corollary 2

Corollary to Double Angle Formula for Cosine

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

where $\cos$ and $\sin$ denote cosine and sine respectively.

Also known as
This identity and Corollary $1$ are sometimes known as Carnot's Formulas, for.

Also see

 * Square of Sine: $\sin^2 \theta = \dfrac {1 - \cos 2 \theta} 2$