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:
 * $\cos^{-1} \left({x}\right) := \left\{{y \in \R: \cos \left({y}\right) = x}\right\}$

where $\cos \left({y}\right)$ is the cosine of $y$.