## Algebra 1: Common Core (15th Edition)

$(3n+20)(3n-20)$
$9n^{2}-400=$ ...write each term as a square. $=(3n)^{2}-20^{2}$ ...factor using the rule for a difference of two squares. ($a^{2}-b^{2}=(a+b)(a-b),\ a=3n,\ b=20$) $=(3n+20)(3n-20)$