$\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ ĐK\ XĐ\ x\geqslant 0;x\neq 1\\ b.\ A=\frac{3x+3\sqrt{x} -3-\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -1\right)} +\frac{\sqrt{x} -2}{\sqrt{x} -1} .\left(\frac{1-1+\sqrt{x}}{1-\sqrt{x}}\right)\\ A=\frac{3x+3\sqrt{x} -3-( x-1)}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -1\right)} +\frac{\sqrt{x} -2}{\sqrt{x} -1} .\frac{\sqrt{x}}{1-\sqrt{x}}\\ A=\frac{2x+3\sqrt{x} -2}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -1\right)} +\frac{\sqrt{x} -2}{\sqrt{x} -1} .\frac{\sqrt{x}}{1-\sqrt{x}}\\ A=\frac{\left( 2\sqrt{x} -1\right)\left(\sqrt{x} +2\right)}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -1\right)} +\frac{\sqrt{x} -2}{\sqrt{x} -1} .\frac{\sqrt{x}}{1-\sqrt{x}}\\ A=\frac{2\sqrt{x} -1}{\sqrt{x} -1} +\frac{\sqrt{x} -2}{\sqrt{x} -1} .\frac{\sqrt{x}}{1-\sqrt{x}}\\ A=\frac{\left( 2\sqrt{x} -1\right)\left( 1-\sqrt{x}\right)}{\left(\sqrt{x} -1\right)\left( 1-\sqrt{x}\right)} +\frac{\sqrt{x} -2}{\sqrt{x} -1} .\frac{\sqrt{x}}{1-\sqrt{x}}\\ A=\frac{-2x+3\sqrt{x} -1+x-2\sqrt{x}}{\left(\sqrt{x} -1\right)\left( 1-\sqrt{x}\right)} =\frac{-x+\sqrt{x} -1}{\left(\sqrt{x} -1\right)\left( 1-\sqrt{x}\right)} \end{array}$
