Answer
$[0,\pi]$, $cos^{-1}(x)$.
Work Step by Step
To have an inverse, a function needs to pass the horizontal line test. For $y=cos(x)$, we need to restrict the domain so that an inverse can be found, and the restricted domain is $[0,\pi]$. We use a special symbol $f^{-1}$ to denote an inverse, and the inverse of $y=cos(x)$ is $y=cos^{-1}(x)$.
