\[ax - 4a = 2x - 8\]
\[ax - 2x = 4a - 8\]
\[x(a - 2) = 4 \bullet (a - 2)\]
\[a = 2 \Longrightarrow x - любое.\]
\[Ответ:\ \ a \in ( - \infty;2) \cup (2;\ + \infty).\]