Answer
$16x^2-\dfrac{4}{9}$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the given expression, $
\left(4x-\dfrac{2}{3}\right)\left(4x+\dfrac{2}{3}\right)
,$ is equivalent to
\begin{array}{l}\require{cancel}
(4x)^2-\left(\dfrac{2}{3}\right)^2
\\\\=
16x^2-\dfrac{4}{9}
.\end{array}
