Answer
$k^{2} - 9$
Work Step by Step
We use the formula for the difference of squares to apply to this question.
The difference of squares formula is:
$(a-b) (a+b) = a^{2} - b^{2}$
In the given formula let k represents a and 3 represents b.
$(k-3) (k+3) = k^{2} - 3^{2}$
= $k^{2} - 9$
