Answer
$85$
Work Step by Step
$\bf{\text{Solution Outline:}}$
To simplify the given expression, $
(6+7i)(6-7i)
,$ use the special product on multiplying the sum and difference of like terms. Then use $i^2=-1.$
$\bf{\text{Solution Details:}}$
Using the product of the sum and difference of like terms which is given by $(a+b)(a-b)=a^2-b^2,$ the expression above is equivalent
\begin{array}{l}\require{cancel}
(6)^2-(7i)^2
\\\\=
36-49i^2
.\end{array}
Since $i^2=-1,$ the expression above is equivalent to
\begin{array}{l}\require{cancel}
36-49(-1)
\\\\=
36+49
\\\\=
85
.\end{array}