for all x ∈ A∩B=> x ∈ A and x ∈B=> x ∈ A ( A is subset of B)=> A∩B is subset of A --(1)and for all x ∈ A=> x ∈ A and x ∈ B ( A is subset of B)=> x ∈ A∩B=> A is subset of A∩B ---(2)from (1)...