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

$k^{2}-9$
$(k-3)(k+3)=$ ...identify which terms correspond to $a$ and $b$ ...in the rule for the product of a sum and difference ($(a+b)(a-b)=a^{2}-b^{2}$) $a=k,\ b=3$ ...substitute for $a$and $b$ in the rule $(k-3)(k+3)=k^{2}-3^{2}$ ...simplify. =$k^{2}-9$