## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$(z+3)(z^2+7)$
Using factoring by grouping, the factored form of the given expression, $z^3+3z^2+7z+21 ,$ is \begin{array}{l} (z^3+3z^2)+(7z+21) \\\\= z^2(z+3)+7(z+3) \\\\= (z+3)(z^2+7) .\end{array}