So sánh hai số sauuuuuu

Ta có:

`M = sqrt(18) - sqrt(8)`

`M = sqrt(9 * 2) - sqrt(4 * 2)`

`M = 3sqrt(2) - 2sqrt(2)`

`M = sqrt(2)`

Ta lại có:

`N = (5 + sqrt(5)) / (sqrt(5) + 1) - sqrt(6 - 2sqrt(5))`

`N = (sqrt(5)(sqrt(5) + 1)) / (sqrt(5) + 1) - sqrt(5 - 2sqrt(5) * 1 + 1)`

`N = sqrt(5) - sqrt((sqrt(5) - 1)^2)`

`N = sqrt(5) - |sqrt(5) - 1|`

Vì `sqrt(5) > 1` nên `sqrt(5) - 1 > 0`

`N = sqrt(5) - (sqrt(5) - 1)`

`N = sqrt(5) - sqrt(5) + 1`

`N = 1` 

Vì `2 > 1` nên `sqrt(2) > sqrt(1)`, do đó `sqrt(2) > 1`

Vậy `M > N`