Đáp án+Giải thích các bước giải:
`sqrt{4+sqrt7}-sqrt{4-sqrt7}`
`=sqrt2(sqrt{4+sqrt7}-sqrt{4-sqrt7}):sqrt2`
`=(sqrt{8+2sqrt7}-sqrt{8-2sqrt7}):sqrt2`
`=(sqrt{7+2sqrt7+1}-sqrt{7-2sqrt+1}):sqrt2`
`=(sqrt{(sqrt7+1)^2}-sqrt{(sqrt7-1)^2}):sqrt2`
`=(|sqrt7+1|-|sqrt7-1|):sqrt2`
`=(sqrt7+1-sqrt7+1):sqrt2`
`=2:sqrt2`
`=2/sqrt2`
`=(2sqrt2)/2`
`=sqrt2`
