Let a be a non-empty set and let s = p(a) be its power set. let b be a non-empty subset of a. on s, we define a relation r as r= {(a1, a2) esx sa, b = a, b} show that r is an equivalence relation. [2 marks] describe the equivalence classes of r when a = z and b = {1,2,3} [2 marks]