\[f(x) = \sqrt{x + 4} + \frac{8}{x^{2} - 9}\]
\[\left\{ \begin{matrix}
x + 4 \geq 0\ \ \\
x² - 9
eq 0 \\
\end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix}
x \geq - 4 \\
x²
eq 9\ \\
\end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix}
x \geq - 4 \\
x
eq \pm 3 \\
\end{matrix} \right.\ \]
\[D(f) = \lbrack - 4; - 3) \cup ( - 3;3) \cup (3; + \infty).\]