The language of set theory is based on a single fundamental relationship called membership . |
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For example, R = {1, 2, 3} is the set R containing 1, 2, and 3 as its members.
A member is related to a set using the symbol
, which means
is an element of
,
is a member of
, or
belongs to
. For set
R
= {1, 2, 3}, 1
R
can be read, 1
is an element of
R
, 1
is a member of
R
, or 1
belongs to
R
. For set
R
, you also know 2
R
and 3
R
.
To identify objects
not
in a set use the symbol
. It means
is
not
an element of
,
is not a member of
, or
does not belong to
. For set
R
= {1, 2, 3}, a possible example is 6
R
, which is read, 6
is not an element of
R
.
A set must be defined properly so you can determine whether an object is a member of the set. There are several ways to do this including written description , roster method , and set notation .
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A is the set of natural numbers below 30 divisible by 5. B is the set of odd digits. C is the set of whole numbers. |
A = {5, 10, 15, 20, 25} B = {1, 3, 5, 7, 9} C = {0, 1, 2, 3, ...} |
A = { x |0 < x < 30, x divisible by 5} B = { x |0 < x < 10, x is odd}
C
= {
x
|
x
|