This lecture is part of my Berkeley math 115 course "Introduction to number theory"
For the other lectures in the course see • Introduction to number theory (Berkeley Ma...
We use Gauss's lemma to find out when -2, 3, 5, are quadratic residues of a prime and give some applications.
The textbook is "An introduction to the theory of numbers" by Niven, Zuckerman, and Montgomery (5th edition).