Some Definitions in Sets
Posted by
Ravi Kumar at Saturday, January 8, 2011
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Null Set:
A set is said to be a null set if it has no elements. It is also called an empty set or a void set and is denoted by ø.
Example:
{x  x is a perfect square and 4< x <9}
Finite and infinite sets:
A set ‘A’ is said to be finite if it is either an empty set or contains finite number of elements. Otherwise it is called an infinite set.
Example:
Set of natural numbers less than 100 is finite.
Cardinality of a finite set:
The number of distinct elements in a set is called the cardinality of the set. If a finite set A has n distinct elements, the cardinality of the set is n and is denoted by O(A) or n(A). The cardinality of an empty set is zero.
Example:
Cardinality of A = {a,e,I,o,u} is 5.