`M=sqrt{9+4sqrt5}-sqrt{6-2sqrt5}`
`=sqrt{(2+sqrt5)^2}-sqrt{(sqrt5-1)^2}`
`=2+sqrt5-(sqrt5-1)`
`=2+sqrt5-sqrt5+1=3`
`N=sqrt{7-4sqrt3}-sqrt{12-6sqrt3}`
`=sqrt{(2-sqrt3)^2}-sqrt{(3-sqrt3)^2}`
`=2-sqrt3-(3-sqrt3)`
`=2-sqrt3-3+sqrt3=-1`
a) Ta có: \(M=\sqrt{9+4\sqrt{5}}-\sqrt{6-2\sqrt{5}}\)
\(=\sqrt{5}+2-\left(\sqrt{5}-1\right)\)
\(=3\)
b) Ta có: \(N=\sqrt{7-4\sqrt{3}}-\sqrt{12-6\sqrt{3}}\)
\(=2-\sqrt{3}-\left(3-\sqrt{3}\right)\)
=-1