Don't you mean (6x^2 - 2)/(x^2 + 1)? You wrote 6x^2 - 2/(x^2+1), which is a completely different thing.-2((1/((x^2 + 1)^2 )) - ((4x^2 )/(x^2 +1)^3 )) = 6x^2-2/(x^2+1)
This is actually the last step of this problem. I understand everything they did up until here, but I'm a bit confused as to how they got from their last step, to the actual answer. Could someone explain?