Let's now show a graphic representation of a complement of a set using a Venn diagram. First of all, a universal set is often shown as a rectangular box. We will call A some subset of the universal set.
intersection of two sets as the overlap in the Venn diagram:
two sets as the entire Venn diagram:
Therefore, symbolically, we write union of the two sets A and B is A ∪ B which means A union B.