0. For each of the following statements, determine if it is true or false. If true, then provide a proof; if false, explain why (for instance, by giving an example in which the statement does not hold).
(a) (17^13) = 5 mod 18
(b) In Z/24Z, the only squares (= classes of the form aa) are 0, 1, 4, 9, 16
(c) Suppose a, b, n ∈ Z and a ≠b. If a^2 = b^2 in Z/nZ, then either gcd(a+b, n) = 1 or gcd(a-b, n) = 1.