\(\Leftrightarrow a^2x-a=4x+2\Leftrightarrow\left(a^2-4\right)x=a+2\)
\(\Leftrightarrow\left(a+2\right)\left(a-2\right)x=a+2\)
a/ Để pt vô nghiệm
\(\Leftrightarrow\left\{{}\begin{matrix}\left(a+2\right)\left(a-2\right)=0\\a+2\ne0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a=\pm2\\a\ne-2\end{matrix}\right.\) \(\Rightarrow a=2\)
b/ Để pt có nghiệm duy nhất
\(\Leftrightarrow\left(a+2\right)\left(a-2\right)\ne0\Rightarrow a\ne\pm2\)