Sine in terms of Hyperbolic Sine

Theorem

 * $\sinh \left({ix}\right) = i \sin x $

where $\sin$ is the sine, $\sinh$ is the hyperbolic sine, and $i^2=-1$.

Also see

 * Cosine in terms of Hyperbolic Cosine
 * Tangent in terms of Hyperbolic Tangent
 * Cotangent in terms of Hyperbolic Cotangent
 * Secant in terms of Hyperbolic Secant
 * Cosecant in terms of Hyperbolic Cosecant