V  Quadratic Reciprocity

1. Introduction. Quadratic congruences, square roots modulo a prime.
2. Quadratic residues and non residues.
3. Euler's Critereon.
4. Gauss' Lemma.
5. The quadratic character of 2:  for which primes  p  does  2  have a square root mod p?
6. Geometric interpretation of Gauss' Lemma.
7. Gauss' Law of Quadratic Reciprocity.