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 $\cos^2 x$

$\blacksquare$

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