$$( y - z ) p + ( z - x ) q = x - y$$
$\left\{\begin{matrix}p=-\frac{qz+y-x-qx}{y-z}\text{, }&y\neq z\\p\in \mathrm{R}\text{, }&\left(y=z\text{ and }q=-1\right)\text{ or }\left(y=x\text{ and }z=x\right)\end{matrix}\right.$
$\left\{\begin{matrix}q=-\frac{-x+py+y-pz}{z-x}\text{, }&z\neq x\\q\in \mathrm{R}\text{, }&z=x\text{ and }\left(p=-1\text{ or }y=x\right)\end{matrix}\right.$
