Đáp án:
`+)C=9/(sqrt10-1)+(5sqrt2-2sqrt5)/(sqrt2-sqrt5)`
`=(9(sqrt10+1))/((sqrt10-1)(sqrt10+1))+(sqrt10(sqrt5-sqrt2))/(sqrt2-sqrt5)`
`=(9(sqrt10+1))/(10-1)+(sqrt10(sqrt5-sqrt2))/(sqrt2-sqrt5)`
`=sqrt10+1-sqrt10=1`
Vậy `C=1`
`+)D=(4+sqrt15)(sqrt10-sqrt6)sqrt(4-sqrt15)`
`=(sqrt10-sqrt6).sqrt(4+sqrt15).sqrt(4+sqrt15).sqrt(4-sqrt15)`
`=(sqrt10-sqrt6).sqrt(4+sqrt15).sqrt((4+sqrt15)(4-sqrt15))`
`=sqrt(sqrt10-sqrt6).sqrt((4+sqrt15)(sqrt10-sqrt6))`
`=sqrt((sqrt10-sqrt6)(sqrt10+sqrt6))`
`=sqrt(10-6)`
`=sqrt4=2`
Vậy `D=2`
