Answer
$x^3+4x^2-20x+7$
Work Step by Step
Using the Distributive Property, the given expression, $
(x+7)(x^2-3x+1)
,$ is equivalent to
\begin{array}{l}\require{cancel}
x(x^2)+x(-3x)+x(1)+7(x^2)+7(-3x)+7(1)
\\\\=
x^3-3x^2+x+7x^2-21x+7
\\\\=
x^3+(-3x^2+7x^2)+(x-21x)+7
\\\\=
x^3+4x^2-20x+7
.\end{array}
