Hyperbolic Cotangent in terms of Cotangent

Theorem

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

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

Also see

 * Sine of Imaginary Number
 * Cosine of Imaginary Number
 * Tangent of Imaginary Number
 * Secant of Imaginary Number
 * Cosecant of Imaginary Number