Đáp án:
a) `M= 3`
b) `N=-2`
Giải thích các bước giải:
a) `M=sqrt{9+4sqrt5}-sqrt{6-2sqrt5}`
`M= sqrt{sqrt(5^2)+2.sqrt5 .2 +2^2} - sqrt{sqrt(5^2)-2.sqrt5 .1+1^2}`
`M= sqrt{(sqrt5+2)^2} - sqrt{(sqrt5-1)^2}`
`M= |sqrt5+2| - |sqrt5-1|`
`M= sqrt5+2-sqrt5+1`
`M= 3`
b) `N=sqrt{8-2sqrt7}-sqrt{8+2sqrt7}`
`N= sqrt{sqrt(7^2)-2.sqrt7 .1+1^2} - sqrt{sqrt(7^2)+2.sqrt7 .1+1^2}`
`N= sqrt{(sqrt7-1)^2}-sqrt{(sqrt7+1)^2}`
`N= |sqrt7-1| - |sqrt7+1|`
`N= sqrt7-1-sqrt7-1`
`N= -2`
