$\left\{\begin{matrix}P=-\frac{Qy+r}{x}\text{, }&x\neq 0\\P\in \mathrm{R}\text{, }&r=-Qy\text{ and }x=0\end{matrix}\right.$

$\left\{\begin{matrix}Q=-\frac{Px+r}{y}\text{, }&y\neq 0\\Q\in \mathrm{R}\text{, }&r=-Px\text{ and }y=0\end{matrix}\right.$