\[\ \frac{a - 2\sqrt{a}}{3\sqrt{a} - 6} = \frac{\sqrt{a}\left( \sqrt{a} - 2 \right)}{3 \cdot (\sqrt{a} - 2)} = \frac{\sqrt{a}}{3}\ \]
\[\frac{5}{3\sqrt{10}} = \frac{5}{3\sqrt{10}} \cdot \frac{\sqrt{10}}{\sqrt{10}} = \frac{5\sqrt{10}}{30} = \frac{\sqrt{10}}{6}\ \]