Definition:Inverse Cosine/Complex/Arccosine

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

where:
 * $\Ln$ 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