Answer
$4m^2+28m+49-4mn-14n+n^2$
Work Step by Step
Using $(a\pm b)^2=a^2\pm2ab+b^2$ or the square of a binomial, the expression, $
[(2m+7)-n]^2
,$ is equivalent to
\begin{array}{l}\require{cancel}
(2m+7)^2-2(2m+7)(n)+(n)^2
\\\\=
(2m+7)^2-4mn-14n+n^2
\\\\=
(2m)^2+2(2m)(7)+(7)^2-4mn-14n+n^2
\\\\=
4m^2+28m+49-4mn-14n+n^2
.\end{array}
