\[t = x^{2} + 2x\]
\[t^{2} - 11t + 24 \leq 0\]
\[(t - 8)(t - 3) \leq 0\]
\[3 \leq t \leq 8 \Longrightarrow 3 \leq x^{2} + 2x \leq 8\]
\[\left\{ \begin{matrix} x^{2} + 2x \geq 3 \\ x^{2} + 2x \leq 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} x^{2} + 2x - 3 \geq 0 \\ x^{2} + 2x - 8 \leq 0 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} (x - 1)(x + 3) \geq 0 \\ (x - 2)(x + 4) \leq 0 \\ \end{matrix} \right.\ \]
\[Ответ:\lbrack - 4; - 3\rbrack \cup \lbrack 1;2\rbrack\text{.\ }\]