Answer
$\dfrac{1}{9}a^{4}-49$
Work Step by Step
$\Big(\dfrac{1}{3}a^{2}-7\Big)\Big(\dfrac{1}{3}a^{2}+7\Big)$
To evaluate this product, use the following formula:
$(x-y)(x+y)=x^{2}-y^{2}$
Here, $x=\dfrac{1}{3}a^{2}$ and $y=7$
$\Big(\dfrac{1}{3}a^{2}-7\Big)\Big(\dfrac{1}{3}a^{2}+7\Big)=\Big(\dfrac{1}{3}a^{2}\Big)^{2}-(7)^{2}=\dfrac{1}{9}a^{4}-49$
