A = {0,1,2,3,4} B = { 0,2,4} C = {2,3,4,5}
a) A∪B = {0,1,2,3,4} A∪C = {0,1,2,3,4,5} B∪C = { 0,2,,,3,4,5}
A∪B∪C = {0,1,2,3,4,5}
b) A∪B = { 1,2,3,4} B∪A = { 0,1,2,3,4} ⇒ A∪B = B∪A
(A∪B)∪C = {0,1,2,3,4} ∪ { 2,3,4,5} = {0,1,2,3,4,5}
A∪(B∪C) + {0,1,2,3,4}∪{2,3,4,5} = {0,1,2,3,4,5}