Introduction to number theory (Berkeley Math 115) - Introduction to number theory lecture 31. Quadratic residues.

This lecture is part of my Berkeley math 115 course "Introduction to number theory" For the other lectures in the course see https://www.youtube.com/playlist?list=PL8yHsr3EFj53L8sMbzIhhXSAOpuZ1Fov8 We cover some basic properties of quadratic residues, and use Gauss's lemma to find the primes for which 2 is. a quadratic residue. The textbook is "An introduction to the theory of numbers" by Niven, Zuckerman, and Montgomery (5th edition).