Сократите дробь: (a-25)/(5+корень из a).

\[\ \frac{a - 25}{5 + \sqrt{a}} = \frac{\left( \sqrt{a} - 5 \right)\left( \sqrt{a} + 5 \right)}{5 + \sqrt{a}} = \sqrt{a} - 5\]

\[\frac{2}{3\sqrt{5} + 1} - \frac{2}{3\sqrt{5} - 1} =\]

\[= \frac{2 \cdot \left( 3\sqrt{5} - 1 \right) - 2 \cdot \left( 3\sqrt{5} + 1 \right)}{45 - 1} =\]

\[= \frac{6\sqrt{5} - 2 - 6\sqrt{5} - 2}{44} = \frac{- 4}{44} = - \frac{1}{11}.\]

\[\ 4\sqrt{2\frac{7}{9}} - 2 = 4 \cdot \sqrt{\frac{25}{9}} - 2 = 4 \cdot \frac{5}{3} - 2 =\]

\[= 6\frac{2}{3} - 2 = 4\frac{2}{3}\]