$\left\{\begin{matrix}a=0\text{, }&x\neq 0\text{ and }x\neq 2b\\a=-\frac{x}{2}+3b\text{, }&x\neq 2b\text{ and }x\neq -2b\end{matrix}\right.$

$\left\{\begin{matrix}a=0\text{, }&x\neq 0\text{ and }x\neq 2b\\a=-\frac{x}{2}+3b\text{, }&|x|\neq 2|b|\end{matrix}\right.$

$\left\{\begin{matrix}b=\frac{x+2a}{6}\text{, }&x\neq a\text{ and }x\neq -\frac{a}{2}\\b\neq \frac{x}{2}\text{, }&a=0\text{ and }x\neq 0\end{matrix}\right.$