## Precalculus (6th Edition) Blitzer

$3x^{2}(x+2)(x-2)$
$3x^{4}-12x^{2}\quad$ ... factor out $3x^{2}$ $=3x^{2}(x^{2}-4)$ The parentheses hold a difference of squares, $x^{2}-2^{2}$, thus: $=3x^{2}(x+2)(x-2)$