Answer
$25m^{2}-1$
Work Step by Step
From Page 301, we know that the product of a sum and difference of two terms $x$ and $y$ is given by the following equation: $(x+y)(x-y)=x^{2}-y^{2}$.
Therefore, $(5m-1)(5m+1)=(5m)^{2}-1^{2}=5^{2}m^{2}-1=25m^{2}-1$.
