~ Bạn tham khảo ~
`B = 2/[x+4] + [x+20]/[x^2-16]`
`=> B = [2(x-4)]/[(x-4)(x+4)] + [x+20]/[x^2-4^2]`
`=> B = [2(x-4)]/[(x-4)(x+4)] + [x+20]/[(x-4)(x+4)]`
`=> B = [2(x-4)+x+20]/[(x-4)(x+4)]`
`=> B = [2x-8+x+20]/[(x-4)(x+4)]`
`=> B = [3x+12]/[(x-4)(x+4)]`
`=> B = [3(x+4)]/[(x-4)(x+4)]`
`=> B = 3/[x-4]`