Answer
$$y=\sqrt{2}\sqrt{x},\:y=-\sqrt{2}\sqrt{x}$$
Work Step by Step
Switching the elements of the domain and the range (in other words, the dependent and independent variables), we find that the inverse is:
$$x=\frac{1}{2}y^2 \\ y=\sqrt{2}\sqrt{x},\:y=-\sqrt{2}\sqrt{x}$$
