Prove or disprove (with a counterexample and explanation) each
of the following claims.
(a) If n is a positive integer and a and b are integers such
that n|ab and n - a, then n|b.
(b) Let a, b, d, n ∈ Z with n ≥ 1. Suppose d > 0. If a ≡ b
(mod n) and d|n, then a ≡ b (mod d).