Đáp án:
`1.`
`(3)/(\sqrt{5})=(3.\sqrt{5})/(\sqrt{5}.\sqrt{5})=(3\sqrt{5})/(5)`
__________________
`(2)/(\sqrt{6})=(2.\sqrt{6})/(\sqrt{6}.\sqrt{6})=(2\sqrt{6})/(6)=(\sqrt{6})/(3)`
__________________
`(2\sqrt{5})/(\sqrt{3})=(2.\sqrt{5}.\sqrt{3})/(\sqrt{3}.\sqrt{3})=(2\sqrt{15})/(3)`
__________________
`(3\sqrt{2})/(\sqrt{6})=(3.\sqrt{2})/(\sqrt{3}.\sqrt{2})=(3)/(\sqrt{3})=\sqrt{3}`
`2.`
`(2)/(\sqrt{7}-\sqrt{5})`
`=(2.(\sqrt{7}+\sqrt{5}))/((\sqrt{7}-\sqrt{5}).(\sqrt{7}+\sqrt{5}))`
`=(2.(\sqrt{7}+\sqrt{5}))/(7-5)`
`=\sqrt{7}+\sqrt{5}`
__________________
`(3)/(\sqrt{11}-\sqrt{8})`
`=(3.(\sqrt{11}+\sqrt{8}))/((\sqrt{11}-\sqrt{8}).(\sqrt{11}+\sqrt{8}))`
`=(3.(\sqrt{11}+\sqrt{8}))/(11-8)`
`=\sqrt{11}+\sqrt{8}`
__________________
`(3)/(\sqrt{11}+\sqrt{8})`
`=(3.(\sqrt{11}-\sqrt{8}))/((\sqrt{11}+\sqrt{8}).(\sqrt{11}-\sqrt{8}))`
`=(3.(\sqrt{11}-\sqrt{8}))/(11-8)`
`=\sqrt{11}-\sqrt{8}`
__________________
Đề 1:
`(2)/(\sqrt{6}+2)`
`=(2.(\sqrt{6}-2))/((\sqrt{6}+2).(\sqrt{6}-2))`
`=(2.(\sqrt{6}-2))/(6-4)`
`=\sqrt{6}-2`
Đề 2:
`(2)/(\sqrt{6}+3)`
`=(2.(\sqrt{6}-3))/((\sqrt{6}+3).(\sqrt{6}-3))`
`=(2.(\sqrt{6}-3))/(6-9)`
`=(-2.(\sqrt{6}-3))/(3)`
`=(6-2\sqrt{6})/(3)`
____________________
`(3)/(\sqrt{6}-3)`
`=(3.(\sqrt{6}+3))/((\sqrt{6}-3).(\sqrt{6}+3))`
`=(3.(\sqrt{6}+3))/(6-9)`
`=(3.(\sqrt{6}+3))/(-3)`
`=-(\sqrt{6}+3)`
`=-3-\sqrt{6}`
