Secant in terms of Hyperbolic Secant

Theorem

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

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

Also see

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