ĐKXĐ:......
1/[tex]\frac{\sqrt{x_{2}+1}-\sqrt{x_{1}+1}}{x_{2}-x_{1}}=\frac{\sqrt{x_{2}+1}-\sqrt{x_{1}+1}}{x_{2}+1-(x_{1}+1)}=\frac{\sqrt{x_{2}+1}+\sqrt{x_{1}+1}}{(\sqrt{x_{2}+1}-\sqrt{x_{1}+1})(\sqrt{x_{2}+1}+\sqrt{x_{1}+1})}\\ =\frac{1}{\sqrt{x_{2}+1}-\sqrt{x_{1}+1}}[/tex]
2/[tex]\frac{\frac{-2x_{2}+1}{x_{2}-2}-\frac{-2x_{1}+1}{x_{1}-2}}{x_{2}-x_{1}}=\frac{(-2x_{2}+1)(x_{1}-2)-(-2x_{1}+1)(x_{2}-2)}{(x_{2}-2)(x_{1}-2)}.\frac{1}{x_{2}-x_{1}}\\ =\frac{-2x_{2}x_{1}+4x_{2}+x_{1}-2+2x_{1}x_{2}-4x_{1}-x_{2}+2}{(x_{2}-2)(x_{1}-2)}.\frac{1}{x_{2}-x_{1}}=\frac{3(x_{2}-x_{1})}{(x_{2}-2)(x_{1}-2)}.\frac{1}{x_{2}-x_{1}}\\ =\frac{3}{(x_{2}-2)(x_{1}-2)}[/tex]