$$\left. \begin{array} { l } { f ( x ) = \sqrt { 2 } y = - 2 x } \\ { \text { i n t e i n t \right.$$
$\left\{\begin{matrix}x=\frac{\sqrt{2}y}{f}\text{, }&f\neq 0\\x\in \mathrm{C}\text{, }&y=0\text{ and }f=0\end{matrix}\right.$
$\left\{\begin{matrix}x=\frac{\sqrt{2}y}{f}\text{, }&f\neq 0\\x\in \mathrm{R}\text{, }&y=0\text{ and }f=0\end{matrix}\right.$
