Question 884424
*[illustration ab2a.bmp]

1. A-B
take away ab from A so you get just a

2. B-A
take away ab from B so you get just b
3. (A^B)U(B-A)
(A^B) is ab
B-A) is b
join them U and we get B 

4. (A^B)U(A-B)
(A^B) is ab
 A-B  a
join them U and we get A