Giúp mik phần `a)` với

`# Ly`

`+)` Với `x ne 0; x ne +-3,` ta có:

     `A= (9/(x^3 - 9x) + 1/(x+3)) : ((x-3)/(x^2 +3x) - x/(3x+9))`

`= [9/(x(x-3)(x+3)) + 1/(x+3)] : [(x-3)/(x(x+3)) - x/(3(x+3))]`

`= (9 + x(x-3))/(x(x-3)(x+3)) : (3(x-3) -x^2)/(3x(x+3))`

`= (9+ x^2 - 3x)/(x(x-3)(x+3)) : (3x -9- x^2)/(3x(x+3))`

`= (x^2 - 3x +9)/(x(x-3)(x+3)) . (3x(x+3))/(-(x^2 - 3x +9))`

`= 3/(-(x-3))`

`= 3/(3-x)`