Halving identity for cosh

Theorem

The following formula holds: $$\cosh \left( \dfrac{z}{2} \right) = \sqrt{ \dfrac{\cosh(z)+1}{2} },$$ where $\cosh$ denotes hyperbolic cosine.

References

• 1964: Milton Abramowitz and Irene A. Stegun: Handbook of mathematical functions ... (previous) ... (next): $4.5.29$