$\left\{\begin{matrix}a=-x\text{, }&x\neq -b\text{ and }x\neq b\\a\neq 0\text{, }&b=0\end{matrix}\right.$

$\left\{\begin{matrix}b=0\text{, }&a\neq 0\\b\in \mathrm{C}\setminus -x,x\text{, }&x=-a\end{matrix}\right.$

$\left\{\begin{matrix}a=-x\text{, }&|x|\neq |b|\\a\neq 0\text{, }&b=0\end{matrix}\right.$

$\left\{\begin{matrix}b=0\text{, }&a\neq 0\\b\in \mathrm{R}\setminus -x,x\text{, }&x=-a\end{matrix}\right.$