Đáp án + Giải thích các bước giải:
`c,`
Ta có : `sqrt(9-sqrt17) . sqrt(9+sqrt17)`
`=sqrt((9-sqrt17).(9+sqrt17))`
`=sqrt(81-17)=sqrt64`
`3sqrt7=sqrt(3^2 . 7)=sqrt63`
Vì : `63<64 to sqrt63<sqrt64`
`to sqrt(9-sqrt17) . sqrt(9+sqrt17) > 3sqrt7`
`d,`
Ta có : `sqrt(5+sqrt13) . sqrt(5-sqrt13)`
`=sqrt((5+sqrt13).(5-sqrt13))`
`=sqrt(25-13)=sqrt12`
`2sqrt5=sqrt(2^2 . 5)=sqrt20`
Vì : `12<20 to sqrt12<sqrt20`
`to sqrt(5+sqrt13) . sqrt(5-sqrt13) < 2sqrt5`