Alright, I've got one more question. Could someone explain how to factor this completely?
$\displaystyle 16z^4-x^4z^4$
Well, we have:
$\displaystyle 16z^4 - x^4z^4$
1. Factor out a $\displaystyle z^4$
$\displaystyle z^4(16 - x^4)$
2. Factor the difference of squares:
$\displaystyle z^4(4 + x^2)(4 - x^2)$
3. Factor the other difference of squares:
$\displaystyle z^4(4 + x^2)((2 + x)(2 - x))$
And there you go.