\[- \frac{1}{6}x^{2} - 4ax - 18a^{2} - 24 = 0\]
\[\left\{ \begin{matrix} - \frac{1}{6} < 0 \\ D \leq 0\ \ \\ \end{matrix} \right.\ \]
\[D = 16a^{2} + \frac{2}{3} \cdot \left( - 18a^{2} - 24 \right) =\]
\[= 16a^{2} - 12a^{2} - 16 =\]
\[= 4a^{2} - 16 \leq 0\]
\[4a^{2} - 16 \leq 0\]
\[a^{2} = 4\]
\[a = \pm 2\]
\[(a + 2)(a - 2) \leq 0\]
\[- 2 \leq a \leq 2.\]
\[Ответ:\lbrack - 2;2\rbrack.\]