\[\frac{1}{\sqrt{2} + \sqrt{5} + \sqrt{7}} =\]
\[= \frac{- \sqrt{70} + 2\sqrt{5} + 5\sqrt{2}}{10 + 10} =\]
\[= \frac{2\sqrt{5} + 5\sqrt{2} - \sqrt{70}}{20}\]