Cosine of 22.5 Degrees

Theorem

 * $\cos 22.5 \degrees = \cos \dfrac \pi 8 = \dfrac 1 2 \sqrt {2 + \sqrt 2}$

where $\cos$ denotes cosine.

Also see

 * Sine of $22.5 \degrees$
 * Tangent of $22.5 \degrees$