Definition:Inverse Cosine/Complex/Definition 1
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Definition
Let $z \in \C$ be a complex number.
The inverse cosine of $z$ is the multifunction defined as:
- $\cos^{-1} \left({z}\right) := \left\{{w \in \C: \cos \left({w}\right) = z}\right\}$
where $\cos \left({w}\right)$ is the cosine of $w$.