Recall from Lesson 1A, that sets can be either intersecting or disjoint. If sets are intersecting, they have common elements.
The elements that are common to
both
set
X
and set
Y
are called the
intersection
of the sets and are denoted by
X
Y
, which is read
intersection of
X
and
Y
or
X
intersection
Y
.
|
Sets A and B are disjoint. If two sets are disjoint, they have no common elements and the Venn diagram has no overlapping parts. Because no elements are common, you can say that the intersection of two disjoint sets is the empty set .
This is written
A
|
B
= { } or
A
.
The
union
of two sets
X
and
Y
is the set of elements that are in set
X
or
in set
Y
or
in both. The union is denoted by
X
Y
and is read
union of
X
and
Y
or
X
union
Y
.
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Sets A and B are disjoint. If two sets are disjoint, they have no common elements and the Venn diagram has no overlapping parts. However, you still can consider the union of the sets. The union of two disjoint sets is all of sets A and B . |