\[\frac{\sqrt{7x - x^{2}}}{4 - x^{2}}\]
\[\left\{ \begin{matrix} 7x - x^{2} \geq 0 \\ 4 - x^{2} \neq 0\ \ \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\left\{ \begin{matrix} x(x - 7) \leq 0 \\ x \neq \pm 2\ \ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \]
\[x(x - 7) \leq 0\]
\[0 \leq x \leq 7.\]
\[\left\{ \begin{matrix} 0 \leq x \leq 7 \\ x \neq \pm 2\ \ \ \ \ \ \\ \end{matrix} \right.\ \]
\[D(y) = \lbrack 0;2) \cup (2;7\rbrack.\]