Đáp án+Giải thích các bước giải:

`c)  (2\sqrt{x})/(\sqrt{x}-3) - ( x + 9\sqrt{x})/( x - 9 )` ĐKXĐ `x >= 0 ; x \ne 9`

`= (2\sqrt{x}(\sqrt{x}+3))/((\sqrt{x}-3)(\sqrt{x}+3)) - ( x + 9\sqrt{x})/((\sqrt{x}-3)(\sqrt{x}+3))`

`= ( 2x + 6\sqrt{x} - x - 9\sqrt{x} )/((\sqrt{x}-3)(\sqrt{x}+3))`

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

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

`= ( \sqrt{x})/(\sqrt{x}+3)`

`d) (\sqrt{x}+3)/(\sqrt{x}+1)+5/(\sqrt{x}-1)+4/(x-1)` ĐKXĐ `x \ne 1 ; x >= 0`

`= ((\sqrt{x}+3)(\sqrt{x}-1))/((\sqrt{x}+1)(\sqrt{x}-1))+(5(\sqrt{x}+1))/((\sqrt{x}-1)(\sqrt{x}+1))+4/((\sqrt{x}-1)(\sqrt{x}+1))`

`= ( x + 2\sqrt{x} - 3 + 5\sqrt{x} + 5 + 4 )/((\sqrt{x}-1)(\sqrt{x}+1))`

`= ( x + 7\sqrt{x} + 6 )/((\sqrt{x}-1)(\sqrt{x}+1))`

`= ((\sqrt{x}+1)(\sqrt{x}+6))/((\sqrt{x}-1)(\sqrt{x}+1))`

`= (\sqrt{x}+6)/(\sqrt{x}-1)`