Bài 3: Cho biểu thức C= -1/x^2-x + x/x+1 a, Rút gọn C Bài 4: Cho biểu thức D= 3/x-3 + 1/x+1 : 4/x-1 a, Rút gọn D

`C = -1/(x^2 - x) + x/(x +1) ( x \ne 0; +-1)`

`= -1/(x(x -1)) + x/(x +1)`

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

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

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

`---`

`D = 3/(x -3) +1/(x +1) : 4/(x -1) ( x \ne 3;+-1)`

`= 3/(x -3) +1/(x +1) * (x- 1)/4`

`= 3/(x -3) + (x -1)/(4(x +1))`

`= (12(x +1))/(4(x -3)(x +1)) + ((x -1)(x -3))/(4(x -3)(x +1))`

`= (12x + 12 + x^2 -3x -x +3)/(4(x -3)(x +1))`

`= (x^2 + 8x +15)/(4(x -3)(x +1))`