~ Gửi bạn nhea ~
`B = x/(x+3) + (2x-1)/(x-3) - (2x^2-x-3)/(x^2-9)`
`= x/(x+3) + (2x-1)/(x-3) - (2x^2-x-3)/((x-3)(x+3))`
`= (x(x-3)+(x+3)(2x-1)-(2x^2-x-3))/((x-3)(x+3))`
`= (x^2-3x+2x^2-x+6x-3-2x^2+x+3)/((x-3)(x+3))`
`= ((x^2-2x^2+2x^2)+(6x-3x+x-x)+(3-3))/((x-3)(x+3))`
`= (x^2+3x)/((x-3)(x+3))`
`= (x(x+3))/((x-3)(x+3))`
`= x/(x-3)`
`->`đpcm