Answer
$(3x+5)^2$
Work Step by Step
The two numbers whose product is $ac=
9(25)=225
$ and whose sum is $b=
30
$ are $\{
15,15
\}$. Using these two numbers to decompose the middle term, then the factored form of the expression, $
9x^2+30x+25
$, is
\begin{array}{l}\require{cancel}
9x^2+15x+15x+25
\\\\=
(9x^2+15x)+(15x+25)
\\\\=
3x(3x+5)+5(3x+5)
\\\\=
(3x+5)(3x+5)
\\\\=
(3x+5)^2
.\end{array}
