Answer
$16-8\sqrt{7x}+7x$
Work Step by Step
Using $a+b=a^2+2ab+b^2$ (or the square of a binomial), the given expression, $
(4-\sqrt{7x})^2
,$ is equivalent to
\begin{array}{l}\require{cancel}
(4)^2+2(4)(-\sqrt{7x})+(-\sqrt{7x})^2
\\\\=
16-8\sqrt{7x}+7x
.\end{array}
