Given polynomials $p(x), q(x)$, and $r(x)$, $p(x)+(q(x)+r(x))=(p(x)+q(x))+r(x)$.
To verify the associative property of addition, begin by finding the sum of the polynomials:
$\begin{array}{l}
(3 x+4)+\left(\left(5 x^2-1\right)+(2 x+6)\right) \\
=\square x^2+\square x+\square
\end{array}$
To verify the associative property of addition, begin by finding the sum of the polynomials:
$\begin{array}{l}
(3 x+4)+\left(\left(5 x^2-1\right)+(2 x+6)\right) \\
=\square x^2+\square x+\square
\end{array}$