#### Answer

$25x^2-80x+64$

#### Work Step by Step

The student just squared the first and last terms, which is not how squaring of binomials is done.
Using the square of a binomial, which is given by $(a+b)^2=a^2+2ab+b^2$ or by $(a-b)^2=a^2-2ab+b^2,$ the expression, $(5x-8)^2,$ above is equivalent to
\begin{array}{l}\require{cancel}
(5x-8)^2
\\\\=
(5x)^2-2(5x)(8)+(8)^2
\\\\=
25x^2-80x+64
.\end{array}