Cosh of a sum

Theorem

The following formula holds: $$\cosh(z_1+z_2) = \cosh(z_1)\cosh(z_2) + \sinh(z_1)\sinh(z_2),$$ where $\cosh$ denotes hyperbolic cosine and $\sinh$ denotes hyperbolic sine.

References

• 1964: Milton Abramowitz and Irene A. Stegun: Handbook of mathematical functions ... (previous) ... (next): $4.5.25$