MAT315 Summer PS4
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Problem Set 4
1. Let p be a prime and d be a positive integer such that d l p - 1. Using Lagrange’s theorem, show that
the congruence
xd - 1 = 0 (mod p)
has exactly d solutions in zp . (Hint: xd - 1 divides xp − 1 - 1).
2. (a) Find all positive integers n such that
n . 2n + 1 = 0 (mod 3).
(b) Let p 3, 5, 7 be a prime. Prove that there are infinitely many integers n satisfying the congruence n . (315)n + 2022 = 0 (mod p).
3. Let p > 5 be a prime. Prove that
p(p + 1) l (p - 1)! + p + 1.
4. Let n be an odd positive integer passing base 3 test, i.e. 3n = 3 (mod n). Prove that also passes the base 3 test.
5. Let f (x) be a polynomial with integer coefficients and p be a prime. Prove that the congruence
f (x) = 0 (mod p2 )
has either p2 solutions or it has at most p2 - p + 1 solutions in zp2 .
6. Let S = {u : 1 s u s n - 1 and gcd(n, u) = 1} be the set of units modulo n, where n > 2. Let’s denote the elements of S by u1 , u2 , . . . , uk, i.e. S = {u1 , u2 , . . . , uk}. Prove that
(a) u1 + u2 + . . . + uk = , and
(b) (u1u2 . . . uk)2 = 1 (mod n).
2022-07-13