Answer
Perfect square, $(9r-5)^{2}$.
Work Step by Step
$81r^{2}-90r+25=$
...write first and last terms as squares.
$=(9r)^{2}-90r+(5)^{2}$
...does the middle term equal $2ab$?
$90r=2\cdot(9r)\cdot(5)$
$=(9r)^{2}-2\cdot(9r)\cdot(5)+(5)^{2}$
...write as the square of a binomial.
$=(9r-5)^{2}$
Perfect square, $(9r-5)^{2}$.
