Using euler or possibly quadratic reciprocity, we can readily decide if an integer a has a quadratic residue modulo a prime p (a) if a has a quadratic residue modulo a prime p and p 3mod 4, show that integer and that a solution to a2 amod p is given by a 4. +1 is an p+1 (b) use part (a) to solve x2 = 7 mod 787.