Cotangent of Complex Number/Formulation 2

Theorem
Let $a$ and $b$ be real numbers.

Let $i$ be the imaginary unit.

Then:
 * $\cot \left({a + b i}\right) = \dfrac {\cot a \coth b - 1} {\cot a - i \coth b}$

where:
 * $\cot$ denotes the cotangent function (real and complex)
 * $\coth$ denotes the hyperbolic cotangent function.

Also see

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