Đáp án:

`g) (x + 9y)/(x^2 - 9y^2) - (3y)/(x^2 + 3xy)`

`= (x + 9y)/((x - 3y)(x + 3y)) - (3y)/(x(x + 3y))`

`= ((x + 9y) . x)/(x(x - 3y)(x + 3y)) - (3y . (x - 3y))/(x(x - 3y)(x + 3y))`

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

`= (x^2 + 6xy + 9y^2)/(x(x - 3y)(x + 3y))`

`= (x + 3y)^2/(x(x - 3y)(x + 3y))`

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

`h) (3x + 2)/(x^2 - 2x + 1) - 6/(x^2 - 1) - (3x - 2)/(x^2 + 2x + 1)`

`= (3x + 2)/(x - 1)^2 - 6/((x - 1)(x + 1)) - (3x - 2)/(x + 1)^2`

`= ((3x + 2) . (x^2 + 2x + 1))/((x - 1)^2(x + 1)^2) - (6(x^2 - 1))/((x - 1)^2(x + 1)^2) - ((3x - 2)(x^2 - 2x + 1))/((x - 1)^2(x + 1)^2)`

`= (3x^3 + 8x^2 + 7x + 2 - 6x^2 + 6 - (3x^3 - 8x^2 + 7x - 2))/((x - 1)^2(x + 1)^2`

`= (3x^3 + 2x^2 + 7x + 8 - 3x^3 + 8x^2 - 7x + 2)/([(x - 1)(x + 1)]^2)`

`= (10x^2 + 10)/(x^2 - 1)^2`