%%visits: 4 ## intuition ## rigour Let b ∈ ℤ which is coprime to p. Then - b is a quadratic_residue mod p $\\iff b^{\frac{p-1}{2}} \equiv 1$ - b is a quadratic_non_residue mod p $\\iff b^{\frac{p-1}{2}} \equiv -1$ ## exam clinic ## examples and non-examples ## resources tags :math: