Đáp án:
$\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ \frac{5x-x\sqrt{x}}{25-x}\\ b.\ \frac{3y\sqrt{y} +2y}{9y-4}\\ c.\ 5\sqrt{3} +5\sqrt{2} \end{array}$
Giải thích các bước giải:
$\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ \frac{x}{5+\sqrt{x}} ;\ ĐKXĐ:x\geqslant 0;\ x\neq 25\\ =\frac{x\left( 5-\sqrt{x}\right)}{\left( 5+\sqrt{x}\right)\left( 5-\sqrt{x}\right)}\\ =\frac{5x-x\sqrt{x}}{25-x}\\ b.\ \frac{y}{3\sqrt{y} -2} ;\ ĐKXĐ:\ y\geqslant 0;\ y\neq \frac{4}{9}\\ =\frac{y\left( 3\sqrt{y} +2\right)}{\left( 3\sqrt{y} -2\right)\left( 3\sqrt{y} +2\right)}\\ =\frac{3y\sqrt{y} +2y}{9y-4}\\ c.\ \frac{5}{\sqrt{3} -\sqrt{2}}\\ =\frac{5\left(\sqrt{3} +\sqrt{2}\right)}{\left(\sqrt{3} -\sqrt{2}\right)\left(\sqrt{3} +\sqrt{2}\right)}\\ =\frac{5\sqrt{3} +5\sqrt{2}}{3-2} =5\sqrt{3} +5\sqrt{2} \end{array}$
