Inverse of $$$y = \cos{\left(x \right)}$$$

To find the inverse function, swap $$$x$$$ and $$$y$$$, and solve the resulting equation for $$$y$$$.

This means that the inverse is the reflection of the function over the line $$$y = x$$$.

If the initial function is not one-to-one, then there will be more than one inverse.

So, swap the variables: $$$y = \cos{\left(x \right)}$$$ becomes $$$x = \cos{\left(y \right)}$$$.

Now, solve the equation $$$x = \cos{\left(y \right)}$$$ for $$$y$$$.

$$$y = \left\{2 \pi n_{1} + \operatorname{acos}{\left(x \right)}\; \middle|\; n_{1} \in \mathbb{Z}\right\}$$$

$$$y = \left\{2 \pi n_{1} - \operatorname{acos}{\left(x \right)}\; \middle|\; n_{1} \in \mathbb{Z}\right\}$$$

$$$y = \left\{2 \pi n_{1} + \operatorname{acos}{\left(x \right)}\; \middle|\; n_{1} \in \mathbb{Z}\right\}$$$A

$$$y = \left\{2 \pi n_{1} - \operatorname{acos}{\left(x \right)}\; \middle|\; n_{1} \in \mathbb{Z}\right\}$$$A

Graph: see the graphing calculator.