>>1088430third step is VERY wrong. you can't just add together powers of x and expect things to work
you can factor out the 2x^2 to get 2x^2(x^2 - 4)
(x^2 - 4) is a difference of squares, so the final is (2x^2) (x + 2) (x - 2)
You can (usually) check with a decently large number like 5. (2 * 5^2)(7)(3) = 1050, and (12 * 5^6 - 48 * 5^4) / (6 * 5^2) = 1050
