Ta có : 

• $\frac{2}{\sqrt{6}-\sqrt{5}}=\frac{2(\sqrt{6}+\sqrt{5})}{6-5}=2(\sqrt{6}+\sqrt{5})$
• $\frac{3}{\sqrt{10}+\sqrt{7}}=\frac{3(\sqrt{10}-\sqrt{7})}{10-7}=\sqrt{10}-\sqrt{7}$
• $\frac{1}{\sqrt{x}-\sqrt{y}}=\frac{\sqrt{x}+\sqrt{y}}{x-y}$
• $\frac{2ab}{\sqrt{a}-\sqrt{b}}=\frac{2ab(\sqrt{a}+\sqrt{b})}{a-b}$