Definition:Inverse Cosine/Real

Definition
Let $x \in \R$ be a real number such that $-1 \le x \le 1$.

The inverse cosine of $x$ is the multifunction defined as:
 * $\map {\cos^{-1} } x := \set {y \in \R: \map \cos y = x}$

where $\map \cos y$ is the cosine of $y$.