Đáp án+Giải thích các bước giải:
`26)sqrt{3+sqrt5}+sqrt{3-sqrt5}-2sqrt{7-3sqrt5}`
`=sqrt{(6+2sqrt5)/2}+sqrt{(6-2sqrt5)/2}-sqrt2.sqrt{14-6sqrt5}`
`=sqrt{(sqrt5+1)^2/2}+sqrt{(sqrt5-1)^2/2}-sqrt2.sqrt{(3-sqrt5)^2}`
`=(sqrt5+1)/sqrt2+(sqrt5-1)/sqrt2-sqrt{2}.(3-sqrt5)`
`=(sqrt5+1+sqrt5-1)/sqrt2-3sqrt2+sqrt(10)`
`=sqrt(10)-3sqrt2+sqrt(10)`
`=2sqrt(10)-3sqrt2`
`29)sqrt{5+sqrt(21)}+sqrt{5-sqrt{21}}-2sqrt{4-sqrt7}`
`=sqrt{(10+2sqrt(21))/2}+sqrt{(10-sqrt(21))/2}-sqrt2sqrt{8-2sqrt7}`
`=sqrt{(sqrt7+sqrt3)^2/2}+sqrt{(sqrt7-sqrt3)^2/2}-sqrt2sqrt{(sqrt7-1)^2}`
`=(sqrt7+sqrt3)/sqrt2+(sqrt7-sqrt3)/2-sqrt2(sqrt7-1)`
`=(2sqrt7)/sqrt2-sqrt(14)+sqrt2`
`=sqrt(14)-sqrt(14)+sqrt2=sqrt2`
