Answer
$9a^4-30a^2y+25y^2$
Work Step by Step
Using $(a+b)^2=a^2+2ab+b^2$, or the special product of the square of a binomial, the given expression, $
(3a^2-5y)^2
,$ is equivalent to
\begin{align*}\require{cancel}
&
(3a^2)^2+2(3a^2)(-5y)+(-5y)^2
\\&=
9a^4-30a^2y+25y^2
.\end{align*}
Hence, the expression $(3a^2-5y)^2$ is equivalent to $9a^4-30a^2y+25y^2$.
