Answer
$64a^6+48a^3+9$
Work Step by Step
Using $(a+b)^2=a^2+2ab+b^2$ or the square of a binomial, the product of the given expression, $
(8a^3+3)^2
,$ is
\begin{array}{l}\require{cancel}
(8a^3)^2+2(8a^3)\left( 3 \right)+\left( 3 \right)^2
\\\\=
64a^6+48a^3+9
.\end{array}
