Номер 535 очень срочно

Решите задачу:

$\frac{a}{3 \sqrt{5}}= \frac{a* \sqrt{5} }{3 \sqrt{5} * \sqrt{5}}= \frac{a \sqrt{5}}{3*5}= \frac{a \sqrt{5} }{15}$

$\frac{4b}{5 \sqrt{c}}= \frac{4b \sqrt{c} }{5 \sqrt{c} \sqrt{c}}= \frac{4b \sqrt{c} }{5c}$

$\frac{6}{ \sqrt{a+b} }= \frac{6\sqrt{a+b}}{(\sqrt{a+b})(\sqrt{a+b})}= \frac{6\sqrt{a+b}}{a+b}$

$\frac{4}{\sqrt{x-y}}= \frac{4\sqrt{x-y}}{(\sqrt{x-y})(\sqrt{x-y})}= \frac{4\sqrt{x-y}}{x-y}$

$\frac{16}{ \sqrt{a}+ \sqrt{6}}= \frac{16(\sqrt{a}+ \sqrt{6})}{(\sqrt{a}+ \sqrt{6})^2}= \frac{16(\sqrt{a}+ \sqrt{6})}{a+2\sqrt{a}\sqrt{6}+6}$

$\frac{a}{ \sqrt{c}-4 }= \frac{a(\sqrt{c}-4)}{(\sqrt{c}-4)(\sqrt{c}-4)}= \frac{a(\sqrt{c}-4)}{c-8 \sqrt{c}+16}$