Half Angle Formulas/Hyperbolic Cosine

Theorem
Let $x \in \R$.

Then:
 * $\cosh \dfrac x 2 = +\sqrt {\dfrac {\cosh x + 1} 2}$

where $\cosh$ denotes hyperbolic cosine.

Proof
As $\forall x \in \R: \cosh x > 0$, the result follows.

Also see

 * Half Angle Formula for Hyperbolic Sine
 * Half Angle Formula for Hyperbolic Tangent