Tangent in terms of Hyperbolic Tangent

Theorem

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

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

Also see

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