Answer
$(7y^2-4)(7y^2+4)$
Work Step by Step
RECALL:
A difference of two square can be factored using the formula
$a^2-b^2=(a-b)(a+b)$
The given binomial can be written as:
$=(7y^2)^2-4^2$
The binomial above is a difference of two squares.
Factor the difference of two squares using the formula above with $a=7y^2$ and $b=4$ to obtain:
$=(7y^2-4)(7y^2+4)$