Question

Let A = {1, 2, 3, 4}, B = {3, 4, 5), what is A ∩ B?

Answer 1

A∆B which is called the symmetric difference between A and B is defined as (A-B)U(B-A).

Now, A-B is the set of all elements which are in A but not in B. So, A - B = {1,2}.

Similarly, B-A is the set of all elements which are in B but not in A. So, B - A = {5}.

Hence A ∆ B = (A-B)U(B-A) = {1,2,5}