#### Answer

$x^{2}-9$

#### Work Step by Step

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