1. SET

2. INTRODUCTION • SET : Set is a basic and unifying idea of mathematics . In fact all mathematical ideas can be expressed in terms of sets. In almost whole of the business mathematics the set theory is applied in one form or the other • Def . of a Set : A set is a collection of well defined and different objects. • POINTS TO REMEMBER : • Element of a Set: Each object of the set is called an element of the set. • Set Notation : Set are generally denoted by capital letters A,B,C. • The elements of sets are denoted mostly by small letters a ,b ,c .

3. SOME EXAMPLES OF SET • The set of days of a week • The set of all month of a year .

4. METHODS OF DESIGNATING A SET • Methods of designating a set : A set can be specified in two following ways.

5. ROASTER METHOD • Def. of Roaster Method : When we represent a set by listing all elements within curly brackets { } seprated by commas , it is called the roaster method . Some examples of roaster method : • A set of vowels : A = { a ,e ,i, o , u } • A set of odd natural numbers : C = {1,3,5,7,….}

6. SET-BUILDER METHOD • Def. of set-builder method : In this method , we do not list all the elements but the set is represented by specifying the defining property Some examples of this method : • A = { x : x is a vowel of English alphabet } • B = { x : x is a positive integer up to 10 } • C = { x / x is an odd positive }

7. TYPES OF SET TYPES OF SET

8. DEFINATION and EXAMPLES • Finite Set : A set is said to be finite if it has finite number of elements . Example : A = { 1,2,3,4 } B = { 2,4,6,8 } • Infinite Set : A set is said to be infinite if it has an infinite number of set . Example : A = {1,2,3 ……} • Null Set : A set which contain no elements , is called null set and is denoted by Ø .

9. Example : A = { x : x is a fraction satisfying x= ¼ } • Equivalent Set : Two finite set A and B are said to be equivalent set if the total number of elements in A is equal to the total number of elements in B . Example : Let A = { 1,2,3,4,5,6 } , B = { 1,2,,7,9,12 } O (A) = 5 = O (B) → A and B are equivalent sets . • Power Set : The power set of a finite set of all sub sets of the given set . Power set A is denoted by P(A) . Example : Take A = {1,2,3,} P (A) = {Ø,{1},{2},{3},{1,2},{1,3},{2,3},{1,2,3} } • Universal Set : If all the sets under consideration are sub sets of a fixed set U ,then U is called a universal set . Example : In plane geometry , the universal set consists of points in a plane .

10. POINTS TO REMEMBER • Complement of a set : Let A be a sub set of universal set U . Then the complement of A is the set of all those element of U which do not belong to A and we denote complement of A by Ac = A’ Example : If U = {2,4,6,8,10} and A = {4,8} Ac = {2,6,10} • Union of two set : If A and B be two given sets , then their union is the set consisting of all the elements of A together with all the elements in B . We should not repeat the elements . The union of two sets A and B is written as A U B . Example :Let A = {1,2,3,5,8} , B = {4,6,7} A U B = {1,2,3,4,5,6,7,8}

11. A B • Diagram of Union of two sets : • Intersection of two sets : The intersection of two sets A and B, denoted by A Π B . Example : Let A = {2,4,6,8} , B = {2,3,5,7} AΠ B = {2} • Diagram of intersection of two sets : A B

12. APPLICATION OF SETS IN PROBLEM • We know that numbers of elements of a finite set A is denoted by n (A) . Following results of number of elements should be kept in mind for doing problems . • n(AUB) = n( A ) + n(B) – n (A Π B) • n(AUB) = n( A ) + n(B) • n(AUB) = n(A - B ) + n(B - A) + n (A Π B) • n( A ) = n(A - B ) + n (A Π B)