a) $\sqrt{\frac{64a²}{25}}$=${\frac{-8a}{5}}$ b) $\sqrt{\frac{(a-2)²}{4a²}}$=${\frac{a-2}{2a}}$ c) ${\frac{\sqrt{15a}}{\sqrt{735a}}}$=$\sqrt{\frac{15a}{735a}}$ = $\sqrt{\frac{1}{49}}$= ${\frac{1}{7}}$ d) ${\frac{\sqrt{2(4-a)²}}{\sqrt{18(a-4)².(a-4)²}}}$ = $\frac{\sqrt{2}|4-a|}{\sqrt{18}|a-4|}$ = $\frac{4\sqrt{2}-a\sqrt{2}}{-a\sqrt{18}+4\sqrt{18}}$
