giup minh voi moi nguoi oi

`a)` Ta có:

`((1 - a\sqrt{a})/(1 - \sqrt{a}) + \sqrt{a}) ((1 - \sqrt{a})/(1 - a))^2  (a >=0 ; a \ne 1)`

`= ((1 - \sqrt{a^3})/(1 - \sqrt{a}) + \sqrt{a})[(1 - \sqrt{a})/((1 - \sqrt{a})(1 + \sqrt{a})^2]]`

`= [((1 - \sqrt{a})(1 + \sqrt{a} + a))/(1 - \sqrt{a}) + \sqrt{a}] (1/(1 + \sqrt{a}))^2`

`= (1 + \sqrt{a} + a + \sqrt{a}) . 1/(1 + \sqrt{a})^2`

`= (1 + 2\sqrt{a} + a) . 1/(1 + \sqrt{a})^2`

`= (1 + \sqrt{a})^2 . 1/(1 + \sqrt{a})^2`

`= 1`

`b) (a + b)/b^2 . \sqrt{(a^2b^4)/(a^2+2ab + b^2)} (a + b > 0 ; b \ne 0)`

`= (a + b)/b^2 . \sqrt{(a^2b^4)/(a + b)^2}`

`= (a + b)/b^2 . \sqrt{(|ab^2|)/(|a+b|)}`

`= (a + b)/b^2 . (|a|b)/(a + b)` do `a + b > 0` và `b^2 >= 0 AA b`

`= |a|`