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

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