Precalculus (6th Edition) Blitzer

$5x(x-3)(x+3)$
Factor out the GCF of $5x$ to obtain: $=5x(x^2-9) \\=5x(x^2-3^2)$ Factor the difference of two squares using the formula $a^2-b^2=(a-b)(a+b)$ to obtain: $=5x(x-3)(x+3)$