Answer
$16x^{2}-49y^{2}$
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 4x represents a and 7y represents b.
$(4x-7y) (4x+7y) = (4x)^{2} - (7y)^{2}$
= $16x^{2}-49y^{2}$
