Cotangent in terms of Hyperbolic Cotangent

Theorem

 * $\coth \left({ix}\right) = -i \cot x $

where $\cot$ is the cotangent function, $\coth$ is the hyperbolic cotangent, and $i^2=-1$.

Also see

 * Sine in terms of Hyperbolic Sine
 * Cosine in terms of Hyperbolic Cosine
 * Tangent in terms of Hyperbolic Tangent
 * Secant in terms of Hyperbolic Secant
 * Cosecant in terms of Hyperbolic Cosecant