~ Bạn tham khảo ~
`B = [4x^2]/[x^2-9] - [x-3]/[x+3] + [x+3]/[x-3]`
`=> B = [4x^2]/[(x-3)(x+3)] - [(x-3)^2]/[(x+3)(x-3)] + [(x+3)^2]/[(x+3)(x-3)]`
`=> B = [4x^2 - (x-3)^2 + (x+3)^2]/[(x-3)(x+3)]`
`=> B = [4x^2 - x^2+6x-9 + x^2 + 6x + 9]/[(x+3)(x-3)]`
`=> B = [4x^2 + 12x]/[(x+3)(x-3)]`
`=> B = [4x(x+3)]/[(x+3)(x-3)]`
`=> B = [4x]/[x-3]`