Answer
$125r^3-150r^2+60r-8$
Work Step by Step
Using $(a+b)^3=a^3+3a^2b+3ab^2+b^3$ or the cube of a binomial, the given expression, $
(5r-2)^3
,$ is equivalent to
\begin{array}{l}\require{cancel}
(5r)^3+3(5r)^2(-2)+3(5r)(-2)^2+(-2)^3
\\\\=
125r^3+3(25r^2)(-2)+3(5r)(4)+(-8)
\\\\=
125r^3-150r^2+60r-8
.\end{array}
