Using one of the reciprocity laws evaluate the quadratic Gauss sum $G(2;p)$. Comparing with the formula $G(2;p)=(2|p)G(1;p)$ deduce that $(2|p)=(-1)^{(p^2-1)/8}$ if $p$ an odd prime.
From Apostol Chapter 9. I can't see what is meant by the initial hint of using one of the reciprocity laws.