let and be relations on z defined as follows: for a; b 2 z, a b if and only if 2 divides a c b. for a; b 2 z, a b if and only if 3 divides a c b. (a) is an equivalence relation on z? if not, is this relation reflexive, symmetric, or transitive? (b) is an equivalence relation on z? if not, is this relation reflexive, symmetric, or transitive?