\[\boxed{\mathbf{558\ (558).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\frac{\sqrt{5}}{\sqrt{5} - 2} = \frac{\sqrt{5} \cdot \left( \sqrt{5} + 2 \right)}{\left( \sqrt{5} + 2 \right)\left( \sqrt{5} - 2 \right)} =\]
\[= \frac{5 + 2\sqrt{5}}{5 - 4} = 5 + 2\sqrt{5}\]
\[2)\ \frac{8}{\sqrt{10} - \sqrt{2}} =\]
\[= \frac{8 \cdot \left( \sqrt{10} + \sqrt{2} \right)}{\left( \sqrt{10} - \sqrt{2} \right)\left( \sqrt{10} + \sqrt{2} \right)} =\]
\[= \sqrt{10} + \sqrt{2}\]
\[3)\ \frac{9}{\sqrt{x} + \sqrt{y}} =\]
\[= \frac{9 \cdot \left( \sqrt{x} - \sqrt{y} \right)}{\left( \sqrt{x} + \sqrt{y} \right)\left( \sqrt{x} - \sqrt{y} \right)} =\]
\[= \frac{9 \cdot \left( \sqrt{x} - \sqrt{y} \right)}{x - y}\]
\[4)\ \frac{2 - \sqrt{2}}{2 + \sqrt{2}} = \frac{\left( 2 - \sqrt{2} \right)^{2}}{\left( 2 + \sqrt{2} \right)\left( 2 - \sqrt{2} \right)} =\]
\[= \frac{\left( 2 - \sqrt{2} \right)^{2}}{2} = \frac{4 - 4\sqrt{2} + 6}{2} =\]
\[= \frac{6 - 4\sqrt{2}}{2} = 3 - 2\sqrt{2}\]
\[\boxed{\mathbf{5}\mathbf{5}\mathbf{8}\mathbf{\text{.\ }}Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ 2\sqrt{4x} + 6\sqrt{16x} - \sqrt{625x} =\]
\[= 4\sqrt{x} + 24\sqrt{x} - 25\sqrt{x} = 3\sqrt{x};\]
\[= 0,9\sqrt{y} - 7,2\sqrt{y} + 3\sqrt{y} =\]
\[= - 3,3\sqrt{y}\]