Rút gọn biểu thức :

`j)` `frac{1}{\sqrt{3}+\sqrt{2}}`

`=frac{\sqrt{3}-\sqrt{2}}{(\sqrt{3}-\sqrt{2})(\sqrt{3}+\sqrt{2})}`

`=frac{\sqrt{3}-\sqrt{2}}{3-2}`

`=\sqrt{3}-\sqrt{2}`

`k)`  `frac{2+\sqrt{3}}{2-\sqrt{3}}`

`=frac{(2+\sqrt{3})(2+\sqrt{3})}{(2-\sqrt{3})(2+\sqrt{3})}`

`=frac{(2+\sqrt{3})^2}{4-3}`

`=(2+\sqrt{3})^2`

`=4+4\sqrt{3}+3`

`=7+4\sqrt{3}`

`l)` `frac{\sqrt{15}-\sqrt{6}}{\sqrt{2}-\sqrt{5}}`

`=frac{\sqrt{3}(\sqrt{5}-\sqrt{2})}{-(\sqrt{5}-\sqrt{2})}`

`=-\sqrt{3}`