Đáp án:

`b) (sqrt{a - 2sqrt{ab} + b})/(sqrt{sqrt{a} - sqrt{b}})`

Điều kiện : `a > b > 0`

` = sqrt{ (a - 2sqrt{ab} + b)/(sqrt{a} - sqrt{b})}`

Ta có: `a - 2sqrt{ab} + b`

` = (sqrt{a})^2 - 2.sqrt{a}.sqrt{b} + (sqrt{b})^2`

` = (sqrt{a} - sqrt{b})^2`

` = sqrt{ ((sqrt{a}-sqrt{b})^2)/(sqrt{a}-sqrt{b})}`

` = sqrt{ sqrt{a} - sqrt{b}}`

`c) (sqrt{x - 3})/(sqrt{sqrt{x} + sqrt{3}}) : (sqrt{sqrt{x} - sqrt{3}})/(sqrt{3})`

Điều kiện : `x > 9`

` = (sqrt{x - 3})/(sqrt{sqrt{x}+sqrt{3}}) . (sqrt{3})/(sqrt{sqrt{x}-sqrt{3}})`

` = (sqrt{3} . sqrt{x - 3})/(sqrt{ (sqrt{x} + sqrt{3})(sqrt{x}-sqrt{3})})`

` = (sqrt{3} . sqrt{x - 3})/(sqrt{x - 3})`

` = sqrt{3}`