Answer
a factor
Work Step by Step
Equating the given expression, $
x+3
,$ to zero and then solving for $x,$ then
\begin{align*}
x+3&=0
\\
x+3-3&=0-3
\\
x&=-3
.\end{align*}
Using $
-3
$ in the synthetic division below, then the remainder is $
0
$ (bottom-right number).
Since the remainder is equal to zero, then $
x+3
$ is a factor of $3x^3+10x^2-x-12$.