1)
`\sqrt{7-4\sqrt3}`
`=\sqrt{7-2.2\sqrt3}`
`=\sqrt{4-2.2.\sqrt3+3}`
`=\sqrt{2^2-2.2.\sqrt3+(\sqrt3)^2}`
`=\sqrt{(2-\sqrt3)^2}`
`=|2-\sqrt3|`
`=2-\sqrt3` (Vì `2>\sqrt3`)
2)
`\sqrt{21-8\sqrt5}`
`=\sqrt{16-2.4\sqrt5+5}`
`=\sqrt{4^2-2.4\sqrt5+(\sqrt5)^2}`
`=\sqrt{(4-\sqrt5)^2}`
`=|4-\sqrt5|`
`=4-\sqrt5` (Vì `4>\sqrt5`)
3)
`\sqrt{28-10\sqrt3}`
`=\sqrt{25-2.5\sqrt3+3}`
`=\sqrt{5^2-2.5\sqrt3+(\sqrt3)^2}`
`=\sqrt{(5-\sqrt3)^2}`
`=|5-\sqrt3|`
`=5-\sqrt3` (Vì `5>\sqrt3`)
4)
`\sqrt{3+\sqrt8}`
`=\sqrt{2+2\sqrt2+1}`
`=\sqrt{(\sqrt2)^2+2.1\sqrt2+1}`
`=\sqrt{(\sqrt2+1)^2}`
`=|\sqrt2+1|`
`=\sqrt2+1`
