Deine Lösung ist richtig
3·(x^2 - 2/x - 4/x^3)^2·(2·x + 2/x^2 + 12/x^4)
= 6·(x^2 - 2/x - 4/x^3)^2·(x + 1/x^2 + 6/x^4)
= 6·((x^5 - 2·x^2 - 4)/x^3)^2·(x^5 + x^2 + 6)/x^4
= 6·(x^5 - 2·x^2 - 4)^2/x^6·(x^5 + x^2 + 6)/x^4
= 6/x^10·(x^5 - 2·x^2 - 4)^2·(x^5 + x^2 + 6)
Das wars.