Answer
$1-49n^2$
Work Step by Step
Using $(a-b)(a+b)=a^2-b^2$, or the product of the sum and difference of like terms, the given expression, $
(1+7n)(1-7n)
,$ is equivalent to
\begin{array}{l}\require{cancel}
(1)^2-(7n)^2
\\\\=
1-49n^2
.\end{array}