\[f(x) = \sqrt{x + 3} + \frac{8}{x^{2} - 36}\]
\[\left\{ \begin{matrix}
x + 3 \geq 0\ \ \ \ \\
x^{2} - 36
eq 0 \\
\end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix}
x \geq - 3\ \ \\
x^{2}
eq 36 \\
\end{matrix}\ \right.\ \Longrightarrow \left\{ \begin{matrix}
x \geq - 3 \\
x
eq \pm 6 \\
\end{matrix} \right.\ \]
\[D(y) = \lbrack - 3;6) \cup (6; + \infty).\]