Union and Intersection

The UNION of two sets is the set of elements which are in either set.

For example: let A = (1,2,3) and let B = (3,4,5). Now the UNION of A and B, written A union B = (1,2,3,4,5). There is no need to list the 3 twice.

The INTERSECTION of two sets is the set of elements which are in both sets.

For example: let A = (1,2,3) and B = (3,4,5). The INTERSECTION of A and B, written A intersection B = (3).

 

Sometimes there will be no intersection at all. In that case we say the answer is the "empty set" or the "null setempty set" null set.

For example: Given set
A =all prime numbers greater than 5 and set B= all even prime numbers,
then A intersect B = empty set.

Now sometimes we want to talk about elements which lie OUTSIDE of a given set and within another set. This is referred to as finding the COMPLEMENT of the set and is written for example, complement symbolB.

In the picture, the red shaded region would represent the complement of set B, complement symbolB.
the complement of set B is the stuff that is in A and outside of B.

Click HERE to enter a world made entirely of Intersections, Unions and Complements. We call it Venn World. You are welcome to help it grow by creating characters your own characters. Our guide the EGG MAN will explain how it is done.

 

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