\[a^{2}x - 12 = 9x + 4a\]
\[a^{2}x - 9x = 4a + 12\]
\[x\left( a^{2} - 9 \right) = 4 \bullet (a + 3)\]
\[x(a - 3)(a + 3) = 4 \bullet (a + 3)\]
\[a = 3 \Longrightarrow нет\ решения.\]
\[a = - 3 \Longrightarrow x - любое.\]
\[Ответ:нет\ решения\ при\ a = 3;\ \ \]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ x - любое\ при\ a = - 3;\]
\[\ \ \ \ \ \ \ \ \ \ \ \ x = \frac{4}{a - 3}\ \ \ при\ a \neq \pm 3.\]