$$f ( x ) f ( - 2 ) = 0 f ( 1 ) = 0$$
$xf^{2}=0$
$\left\{\begin{matrix}\\x=0\text{, }&\text{unconditionally}\\x\in \mathrm{R}\text{, }&f=0\end{matrix}\right.$
$\left\{\begin{matrix}\\f=0\text{, }&\text{unconditionally}\\f\in \mathrm{R}\text{, }&x=0\end{matrix}\right.$
