Đáp án:
`25)sqrt{9+sqrt(56)}=sqrt{9+2sqrt(14)}=sqrt{7+2.sqrt2.sqrt7+2}=sqrt{(sqrt7+sqrt2)^2}=sqrt7+sqrt2` $\\$ `26)sqrt{7+sqrt(24)}=sqrt{7+2sqrt6}=sqrt{6+2sqrt6+1}=sqrt{(sqrt6+1)^2}=sqrt6+1` $\\$ `27)sqrt{3-sqrt5}=sqrt{(6-2sqrt5)/2}=sqrt{(5-2sqrt5+1)/2}=sqrt{(sqrt5-1)^2/2}=(sqrt5-1)/sqrt2=(sqrt{10}-sqrt2)/2` $\\$ `28)sqrt{4+sqrt7}=sqrt{(8+2sqrt7)/2}=sqrt{(7+2sqrt7+1)/2}=sqrt{(sqrt7+1)^2/2}=(sqrt7+1)/sqrt2=(sqrt(14)+sqrt2)/2` $\\$ `29)sqrt{5+sqrt(21)}=sqrt{(10+2sqrt(21))/2}=sqrt{(7+2sqrt3.sqrt7+3)/2}=sqrt{(sqrt7+sqrt3)^2/2}=(sqrt7+sqrt3)/sqrt2=(sqrt(14)+sqrt6)/2` $\\$ `30)sqrt{6-sqrt(35)}=sqrt{(12-2sqrt(35))/2}=sqrt{(7-2sqrt5.sqrt7+5)/2}=sqrt{(sqrt7-sqrt5)^2/2}=(sqrt7-sqrt5)/sqrt2=(sqrt(14)-sqrt(10))/2` $\\$ `31)sqrt{7+sqrt{40}}=sqrt{7+2sqrt(10)}=sqrt{5+2sqrt5.sqrt2+2}=sqrt{(sqrt5+sqrt2)^2}=sqrt5+sqrt2` $\\$ `32)sqrt{8+sqrt(15)}=sqrt{(16+2sqrt(15))/2}=sqrt{(15+2sqrt(15)+1)/2}=sqrt{(sqrt(15)+1)^2/2}=(sqrt(15)+1)/sqrt2=(sqrt{30}+sqrt2)/2` $\\$ `33)sqrt{9+sqrt(77)}+sqrt{(18+2sqrt(77))/2}=sqrt{(11+2sqrt{11}.sqrt7+7)/2}=sqrt{(sqrt(11)+sqrt7)^2/2}=(sqrt(11)+sqrt7)/sqrt2=(sqrt(22)+sqrt(14))/2` $\\$ `34)sqrt{10-sqrt(99)}=sqrt{(20-2sqrt{99})/2}=sqrt{(11-2sqrt{11}.3+9)/2}=sqrt{(sqrt(11)-3)^2/2}=(sqrt(11)-3)/sqrt2=(sqrt(22)-3sqrt2)/2` $\\$ `35)sqrt{7-2sqrt6}=sqrt{6-2sqrt6+1}=sqrt{(sqrt6-1)^2}=sqrt6-1` $\\$ `36)sqrt{13-4sqrt3}=sqrt{12-2.2sqrt3+1}=sqrt{(2sqrt3-1)^2}=2sqrt3-1`
