`3)\sqrt{8-2\sqrt{15}}`
`=\sqrt{(\sqrt{5}-\sqrt{3})^2}`
`=\sqrt{5}-\sqrt{3}`
`4)\sqrt{8+2\sqrt{15}}`
`=\sqrt{(\sqrt{5}+\sqrt{3})^2}`
`=\sqrt{5}+\sqrt{3}`
`5)\sqrt{5-2\sqrt{6}}`
`=\sqrt{(\sqrt{3}-\sqrt{2})^2}`
`=\sqrt{3}-\sqrt{2}`
`6)\sqrt{5+2\sqrt{6}}`
`=\sqrt{(\sqrt{3}+\sqrt{2})^2}`
`=\sqrt{3}+\sqrt{2}`
`9)\sqrt{11-2\sqrt{30}}`
`=\sqrt{(\sqrt{6}-\sqrt{5})^2}`
`=\sqrt{6}-\sqrt{5}`
`12)\sqrt{11+2\sqrt{30}}`
`=\sqrt{(\sqrt{6}+\sqrt{5})^2}`
`=\sqrt{6}+\sqrt{5}`
`13)\sqrt{7-2\sqrt{10}}`
`=\sqrt{(\sqrt{5}-\sqrt{2})^2}`
`15)\sqrt{8+2\sqrt{15}}`
`->`Giống câu `4`
`16)\sqrt{10-2\sqrt{30}}`
`=\sqrt{(\sqrt{5}-\sqrt{2})^2}`
`=\sqrt{5}-\sqrt{2}`
`17)\sqrt{11+2\sqrt{18}}`
`=\sqrt{(3+\sqrt{2})^2}`
`=3+\sqrt{2}`
`18)\sqrt{7+2\sqrt{10}}`
`=\sqrt{(\sqrt{5}+\sqrt{2})^2}`
`=\sqrt{5}+\sqrt{2}`
`20)\sqrt{10-2\sqrt{35}}`
`=\sqrt{(\sqrt{7}-\sqrt{5})^2}`
`=\sqrt{7}-\sqrt{5}`
`22)\sqrt{16-2\sqrt{55}}`
`=\sqrt{(\sqrt{11}-\sqrt{5})^2}`
`=\sqrt{11}-\sqrt{5}`
`23)\sqrt{14-2sqrt{33}}`
`=\sqrt{(\sqrt{11}-\sqrt{3})^2}`
`=\sqrt{11}-\sqrt{3}`
`25)\sqrt{12+2\sqrt{35}}`
`=\sqrt{(\sqrt{7}+\sqrt{5})^2}`
`=\sqrt{7}+\sqrt{5}`
`27)\sqrt{16+2\sqrt{55}}`
`=\sqrt{(\sqrt{11}+\sqrt{5})^2}`
`=\sqrt{11}+\sqrt{5}`
`28)\sqrt{25-4\sqrt{6}}`
`=\sqrt{(\sqrt{24}-1)^2}`
`=\sqrt{24}-1`
`=2\sqrt{6}-1`
