Textbook Problem

In 9-11, prove each of the given statements, assuming that a,b,c,d, and n are integers with $n>1$and that $a=c\left(\mathrm{mod}n\right)$and $b=d\left(\mathrm{mod}n\right)$.

$a^2=c^2\left(\mathrm{mod}n\right)$