Power Reduction Formulas/Cosine Squared/Proof 1

Theorem

$\cos^2 x = \dfrac {1 + \cos 2 x} 2$

Proof

\(\ds 2 \cos^2 x - 1\)

\(=\)

\(\ds \cos 2 x\)

Double Angle Formula for Cosine: Corollary $1$

\(\ds \cos^2 x\)

\(=\)

\(\ds \frac {1 + \cos 2 x} 2\)

solving for $\cos^2 x$

$\blacksquare$