Definition:Inverse Cosine/Complex/Arccosine

Definition
The principal branch of the complex inverse cosine function is defined as:
 * $\arccos^{-1} \left({z}\right) = \dfrac 1 i \ln \left({z + \sqrt{z^2 - 1} }\right)$

Also see

 * Derivation of Complex Arcsine from Inverse Cosine Multifunction