`bb(b o t)`

`sqrt{21 - 6sqrt6} + sqrt{9 +2sqrt18} - sqrt{2sqrt{6 +3sqrt3}} `

Ta có `:`

`sqrt{21 - 6sqrt6} = sqrt{(3sqrt2 - sqrt3)^2} = 3sqrt2 - sqrt3`

`sqrt{9 + 2sqrt18} = sqrt{9 + 6sqrt2} = sqrt{(sqrt6 + sqrt3)^2} = sqrt6 + sqrt3`

`sqrt{2sqrt{6 + 3sqrt3}} = sqrt{sqrt{24 + 12sqrt3}} = sqrt{sqrt{(3sqrt2 + sqrt6)^2}} = sqrt{3sqrt2 + sqrt6}`

`to VT = (3sqrt2 - sqrt3) + (sqrt6 + sqrt3) - sqrt{3sqrt2 + sqrt6}`

`VT = 3sqrt2 +sqrt6 - sqrt{3sqrt2 + sqrt6}`

Vì `3sqrt2 + sqrt6 > 1`

`to (3sqrt2 + sqrt6) > sqrt{3sqrt2 + sqrt6} `

`to VT = (3sqrt2 +sqrt6) - sqrt{3sqrt2 +sqrt6} > 0`

`to` Đề sai `.`

`VT = sqrt{4 + sqrt{5sqrt3 + 5sqrt{48 - 10sqrt{7 + 4sqrt3}}}}`

Ta có `:`

`sqrt{7 + 4sqrt3} = sqrt{(2 + sqrt3)^2} = 2 + sqrt3`

`sqrt{48 - 10sqrt{7 + 4sqrt3}} = sqrt{48 - 10(2 + sqrt3)} = sqrt{28 - 10sqrt3} = sqrt{(5 - sqrt3)^2} = 5 - sqrt3`

`sqrt{5sqrt3 + 5sqrt{48 - 10sqrt{7 + 4sqrt3}}} = sqrt{5sqrt3 + 5(5 - sqrt3)} = sqrt{5sqrt3 + 25 - 5sqrt3} = sqrt{25} = 5`

`VT = sqrt{4 + 5} = sqrt9 = 3 = VP (đpcm) .`