Hyperbolic Cotangent of Sum

Theorem

 * $\coth \left({a + b}\right) = \dfrac {\coth a \coth b + 1} {\coth b + \coth a}$

where $\coth$ denotes the hyperbolic cotangent.

Also see

 * Hyperbolic Sine of Sum
 * Hyperbolic Cosine of Sum
 * Hyperbolic Tangent of Sum