6. Сократите дробь: a) \frac{\sqrt{3}-3}{\sqrt{5}-\sqrt{15}}; 6) \frac{a-2√a}{3√a-6}

a) $$\frac{\sqrt{3}-3}{\sqrt{5}-\sqrt{15}} = \frac{\sqrt{3}(1-\sqrt{3})}{\sqrt{5}(1-\sqrt{3})} = \frac{\sqrt{3}}{\sqrt{5}} = \frac{\sqrt{15}}{5}$$

Ответ: $$\frac{\sqrt{15}}{5}$$

б) $$\frac{a-2\sqrt{a}}{3\sqrt{a}-6} = \frac{\sqrt{a}(\sqrt{a}-2)}{3(\sqrt{a}-2)} = \frac{\sqrt{a}}{3}$$

Ответ: $$\frac{\sqrt{a}}{3}$$