Hyperbolic Secant in terms of Secant

Theorem

 * $\sec \left({ix}\right) = \operatorname{sech} x $

where $\sec$ is the secant function, $\operatorname{sech}$ is the hyperbolic secant, and $i^2=-1$.

Also see

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