\[\sqrt{x^{2} - 4} + \sqrt{1 - \frac{1}{25}x^{2}}\]
\[\left\{ \begin{matrix} (x + 2)(x - 2) \geq 0 \\ (x + 5)(x - 5) \leq 0 \\ \end{matrix} \right.\ \]
\[(x + 2)(x - 2) \geq 0\]
\[x \leq - 2;\ \ x \geq 2.\]
\[(x + 5)(x - 5) \leq 0\]
\[- 5 \leq x \leq 5.\]
\[\left\{ \begin{matrix} x \leq - 2;\ \ x \geq 2 \\ - 5 \leq x \leq 5\ \ \ \ \ \ \\ \end{matrix} \right.\ \]
\[D(y) = \lbrack - 5;\ - 2\rbrack \cup \lbrack 2;5\rbrack.\]