Hyperbolic Tangent in terms of Tangent

Theorem

 * $\tan \left({ix}\right) = i \tanh x $

where $\tan$ is the tangent function, $\tanh$ is the hyperbolic tangent, and $i^2=-1$.

Also see

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