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A set is generally described as a well defined collection of distinct objects.By a well defined collection is meant a collection which is such that,given any object,we may be able to decide whether the object belongs to the collection or not.By distinct objects we mean objects objects no two of which are identical.
Elements or members of set:
The objects in a set are called its members or elements.Capital Letters A,B,C,X,Y,Z etc.,are generally used as names of sets and small letters a,b,c,d,x,y,z etc are used as members of sets.
E.g N = The set of all natural numbers = {1,2,3,...}
      W= The set of whole numbers = {0,1,2,3,...}
Ways of describing a set:There are three different ways of describing a set
1.The Descriptive Method:
A set may be described in words.for example,the set of all vowels of English alphabets.
2.The Tabular Method:
 A set may be described by listing its elements within brackets
{a,e,i,o,u}