Definition:Inverse Cosine/Complex/Arccosine

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

where:
 * $\operatorname{Ln}$ denotes the principal branch of the complex natural logarithm
 * $\sqrt{z^2 - 1}$ denotes the principal square root of $z^2 - 1$.

Also see

 * Derivation of Complex Arcsine from Inverse Cosine Multifunction