Euler's Criterion: Proof and Example

Proof that quadratic residues always have even index:    • Quadratic Residues Always Have Even Index   Intro to indices:    • How to use "Log" in Modular Arithmetic: In...   Euler's criterion is one way to determine whether a number is a quadratic residue mod p. Here we prove Euler's criterion and give an explanation for why it works. Like with many things in number theory, indices and primitive roots will help us out! Quadratic Residues playlist:    • Quadratic Residues   0:00 Proof 6:34 Example Subscribe to see more new math videos! Music: OcularNebula - The Lopez