\[y = x\left( 1 - \sqrt{2} \right);\ \ \ \ \]
\[\lbrack 4 - 4\sqrt{2};3 - 3\sqrt{2}\rbrack\]
\[4 - 4\sqrt{2} \leq x\left( 1 - \sqrt{2} \right) \leq 3 - 3\sqrt{2}\]
\[\frac{4 \cdot \left( 1 - \sqrt{2} \right)}{1 - \sqrt{2}} \leq x \leq \frac{3 \cdot \left( 1 - \sqrt{2} \right)}{1 - \sqrt{2}}\ \]
\[1 - \sqrt{2} < 0\ \ \]
\[3 \leq x \leq 4\]
\[Ответ:\ \ \lbrack 3;4\rbrack.\]