Hyperbolic Cosine of Sum

Theorem

 * $\cosh \paren {a + b} = \cosh a \cosh b + \sinh a \sinh b$

where $\sinh$ denotes the hyperbolic sine and $\cosh$ denotes the hyperbolic cosine.

Also see

 * Hyperbolic Sine of Sum
 * Hyperbolic Tangent of Sum
 * Hyperbolic Cotangent of Sum