$$\left. \begin{array} { l } { \quad ( y + z ) p + ( z + x ) q = x + y } \\ { \quad z ^ { 2 } ( p ^ { 2 } z ^ { 2 } + q ^ { 2 } + q ^ { \right.$$
$\left\{\begin{matrix}x=-\frac{py-y+pz+qz}{q-1}\text{, }&q\neq 1\\x\in \mathrm{R}\text{, }&\left(y=-\frac{z\left(p+1\right)}{p-1}\text{ and }q=1\text{ and }p\neq 1\right)\text{ or }\left(z=0\text{ and }p=1\text{ and }q=1\right)\end{matrix}\right.$
