Đáp án:
`=sqrt7-sqrt6+sqrt3`
Giải thích các bước giải:
`\sqrt{10-2\sqrt{21}}-\sqrt{9-2\sqrt18}+\sqrt3`
`=\sqrt{7-2\sqrt{7.3}+3}-\sqrt{9-6\sqrt2}+\sqrt3`
`=\sqrt{(sqrt7-sqrt3)^2}-sqrt{3(3-2sqrt2)}+sqrt3`
`=|sqrt7-sqrt3|+sqrt3-sqrt{3(2-2sqrt2+1)}`
`=sqrt7-sqrt3+sqrt3-sqrt{3(sqrt2-1)^2}`
`=sqrt7-sqrt{3}(sqrt2-1)`
`=sqrt7-sqrt6+sqrt3`