$\displaystyle \begin{array}{{>{\displaystyle}l}} a)\sqrt{27.48( 1-a)^{2}} \ a< 1\ \\ \sqrt{3.9.3.16( 1-a)^{2}} \ \\ =9.4|1-a|\\ =36( 1-a) =36-36a( a< 1) \ \\ b)\frac{1}{a-b}\sqrt{a^{4}( a-b)^{2}} \ a< b\ \\ \frac{1}{a-b} .a^{2} |a-b|\\ =\frac{1}{a-b} .a^{2}( b-a) \ ( b >a) \ \\ =-a^{2} \ \\ c)\sqrt{\frac{2a}{3}} .\sqrt{\frac{3a}{8}} \ ( a\geqslant 0\ ) \ \\ \rightarrow \sqrt{\frac{2a.3a}{3.8}} =\sqrt{\frac{a^{2}}{4}} =\left| \frac{a}{2}\right| =\frac{a}{2} \ \\ d) \ \sqrt{5a} .\sqrt{45a} -3a.\ a\geqslant 0\ \\ \sqrt{5.5.9a} -3a=15a-3a=12a\ \\ e)\frac{a-b}{\sqrt{a} -\sqrt{b}} -\frac{\sqrt{a^{3}} +\sqrt{b^{3}}}{a-b} \ \\ \sqrt{a} +\sqrt{b} -\frac{\left(\sqrt{a} +\sqrt{b}\right)\left( a-\sqrt{ab} +b\right)}{a-b} \ \\ =\sqrt{a} +\sqrt{b} -\frac{a-\sqrt{ab} +b}{\sqrt{a} -\sqrt{b}} \ \\ =\frac{a-b-a+\sqrt{ab} -b}{\sqrt{a} -\sqrt{b}} =\frac{-2b+\sqrt{ab}}{\sqrt{a} -\sqrt{b}} \ \\ ( \ câu\ này\ nên\ xem\ lại\ đề,\ rút\ gọn\ xấu\ quá\ ) \ \\ \\ \\ \ \end{array}$
