set: we defined collection of distinct objects is called a set. descriptive method:a method by which a set is tabular method: in this form we have to write all the elements of a set within the braces. for example.the set of all natural numbers can be written as, n={1,2,3, 4..... }. set builder form: in this form we use a letter or symbols for an arbitrary element of set and also write the property that is common to all elements.for example, the set of of natural numbers. can be written as, n={x\x is any natural numbers}. finite set: a set having finite number of elements e,g. a= { 1,2,3,4, .,,......50}. members ship of a set: the symbols used for a member ship of the set is € is read as belong to thus a€a mean a is an element of a set.if a is not an element of set a.it is written as a a@a.