1. ??????? when p is prime [[p-1],[n]]=(-1)n, 1<=n<=p-1. prove please.
2. Find the solution of the following system of congruences.
(1) x ? 2 (mod 9)
x ? 11 (mod 15)
(2) x ? 2 (mod 9)
x ? 11 (mod 15)
x ? 16 (mod 25)
3. Find the solution of the following quadratic congruence
(1) x2 + 7x + 10 ? 0 (mod 15)
(2) x2 + 10x + 21 ? 0 (mod 17 · 23)
(3) x2 + 5x ? 0 (mod 6)
(4) x2 + 7x ? 0 (mod 8)