$$\frac{1000\ x+xR^{2}-10000\ x}{10000}=\frac{xR4}{100}$$
$\left\{\begin{matrix}\\R_{4}=\frac{R^{2}-9000}{100}\text{, }&\text{unconditionally}\\R_{4}\in \mathrm{C}\text{, }&x=0\end{matrix}\right.$
$\left\{\begin{matrix}\\R_{4}=\frac{R^{2}-9000}{100}\text{, }&\text{unconditionally}\\R_{4}\in \mathrm{R}\text{, }&x=0\end{matrix}\right.$
$\left\{\begin{matrix}\\R=-10\sqrt{R_{4}+90}\text{; }R=10\sqrt{R_{4}+90}\text{, }&\text{unconditionally}\\R\in \mathrm{C}\text{, }&x=0\end{matrix}\right.$
$\left\{\begin{matrix}R=10\sqrt{R_{4}+90}\text{; }R=-10\sqrt{R_{4}+90}\text{, }&R_{4}\geq -90\\R\in \mathrm{R}\text{, }&x=0\end{matrix}\right.$
