42.Let a, b Z, A = {x Z | a divides x}, and B = {x Z | b divides x}. Prove that A B {x Z | gcd(a, b) divides x}.

63.If relation s on Q is defined by

xsy x y Z and is an equivalence relation, then:

(a) List 3 elements in the equivalence class c(1/3).

(b) List 3 elements in the equivalence class c (4)

(c) List 3 elements NOT in the equivalence class c(1/3)

(d) List 3 elements in the equivalence class c (2/3)