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

$4a^2-28a$
Using $a(b+c)=ab+ac$ or the Distributive Property, the given expression, $(a-7)4a$, is equivalent to \begin{array}{l}\require{cancel} 4a(a-7) \\\\= 4a(a)+4a(-7) \\\\= 4a^2-28a .\end{array}