Cosine of i

Theorem

 * $\cos i = \dfrac e 2 + \dfrac 1 {2 e}$

where $\cos$ denotes the complex cosine function and $i$ is the imaginary unit.

Also see

 * Sine of $i$
 * Tangent of $i$
 * Cotangent of $i$
 * Secant of $i$
 * Cosecant of $i$