`C = ( (\sqrt{x}-2)/(x-1) - (\sqrt{x}+2)/(x+2\sqrt{x}+1)) . ((1-x)^2)/2`

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

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

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

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

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

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

` = - \sqrt{x} (\sqrt{x} - 1)`

` = \sqrt{x}  -x`

`a)`

`C=((\sqrt{x}-2)/(x-1)-(\sqrt{x}+2)/(x+2\sqrt{x}+1)).(1-x)^2/2`

Điều kiện xác định : `xne1` và `xge0` 

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

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

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

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

`=-\sqrt{x}.(\sqrt{x}-1)`

`=-x+\sqrt{x}`