$\\$
`7,`
`(x+2)/(x-1) +3/(x+1) - x^2/(x^2 -1)` (Điều kiện : `x \ne ±1`)
`= ( (x+2)(x+1) )/( (x-1)(x+1) ) + (3 (x-1) )/( (x+1)(x-1) - x^2/(x^2 -1)`
`= ( x^2 +3x+2)/( x^2 - 1) + (3x - 3)/(x^2 - 1) - x^2/(x^2 -1)`
`= (x^2 + 3x + 2 + 3x- 3 - x^2)/(x^2 -1)`
`= (6x-1)/(x^2 -1)`
$\\$
`8,`
`(x+1)/(x-3) -2/(x+3) - (4x)/(9-x^2)` (Điề kiện : `x \ne ±3`)
`= ( (x+1) (x+3) )/( (x-3)(x+3) ) - (2 (x-3) )/( (x-3)(x+3) ) + (4x)/(x^2 - 9)`
`= ( x^2 +3x + x+3)/(x^2 - 9) - (2x-6)/(x^2 - 9) +(4x)/(x^2 -9)`
`= (x^2 +4x+3)/(x^2 - 9) - (2x-6)/(x^2 - 9) + (4x)/(x^2 - 9)`
`= (x^2 +4x+3 - 2x+6 +4x)/(x^2 - 9)`
`= (x^2 + 6x + 9)/( (x-3)(x+3) )`
`= ( (x+3) (x+3) )/( (x-3)(x+3) )`
`= (x+3)/(x-3)`
