Answer
$a^2+a-42$
Work Step by Step
Using $(a+b)(c+d)=ac+(ad+bc)+bd$, or the FOIL Method, the given expression, $
(a+7)(a-6)
,$ is equivalent to
\begin{array}{l}\require{cancel}
a^2+(-6a+7a)-42
\\\\=
a^2+a-42
.\end{array}
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