Answer
$9x^2-\dfrac{1}{4}$
Work Step by Step
Using the special product of the sum and difference of like terms, $(a+b)(a-b)=a^2-b^2$, the given expression is equivalent to
\begin{align*}
&
\left( 3x+\dfrac{1}{2} \right)\left( 3x-\dfrac{1}{2} \right)
\\\\&
(3x)^2-\left( \dfrac{1}{2} \right)^2
\\\\&
9x^2-\dfrac{1}{4}
.\end{align*}
