Answer
$25r^{2}-70rs+49s^{2}$
Work Step by Step
From Page 302, we know that the square of a binomial difference $x-y$ is given by the following equation:
$(x-y)^{2}=x^{2}-2xy+y^{2}$
Therefore, $(5r-7s)^{2}=(5r)^{2}-2(5r)(7s)+(7s)^{2}=5^{2}r^{2}-70rs+7^{2}s^{2}=25r^{2}-70rs+49s^{2}$.
