Resonance -Sets Relations and Functions

Target : JEE(IITs)

Set, Relation & Binary Operation

Class : XII

Sets, Relations & Binary Operations

CONTENT Topic Name

Page No.

Theory

01 - 10

Exercise # 1

Objective Questions

11 - 14

Exercise # 2

Subjective Questions

14 - 15

Exercise # 3

IIT-JEE & AIEEE Problems (Provious Years)

15 - 16

Answers

17 - 17

Advanve Level Problems

Subjective Questions

Answers

18 - 18 18 - 18

Syllabus : Proposed ISEET (IIT-JEE / AIEEE) 2012 Sets, Relation & Binary operations : Sets and their representation; Union, intersection and complement of sets and their algebraic properties; Power set; Relation, Types of relations, equivalence relations. Note : This topic was not in JEE upto 2012.

CCXIIISEET

SETS, RELATIONS AND BINARY OPERATIONS SETS SET A set is a collection of well defined objects which are distinct from each other. Set are generally denoted by capital letters A, B, C, ........ etc. and the elements of the set by small letters a, b, c ....... etc. If a is an element of a set A, then we write a  A and say a belongs to A. If a does not belong to A then we write a  A, e.g. the collection of first five prime natural numbers is a set containing the elements 2, 3, 5, 7, 11.

METHODS TO WRITE A SET : (i) Roster Method or Tabular Method : In this method a set is described by listing elements, separated by commas and enclose then by curly brackets. Note that while writing the set in roster form, an element is not generally repeated e.g. the set of letters of word SCHOOL may be written as {S, C, H, O, L}. (ii) Set builder form (Property Method) : In this we write down a property or rule which gives us all the element of the set. A = {x : P(x)} where P(x) is the property by which x  A and colon ( : ) stands for ‘such that’ Example # 1 : Express set A = {x : x  N and x = 2n for n  N} in roster form Solution : A = {2, 4, 6,.........} Example # 2 : Express set B = {x2 : x < 4, x  W} in roster form Solution : B = {0, 1, 4, 9} Example # 3 : Express set A = {2, 5, 10, 17, 26} in set builder form Solution : A = {x : x = n2 + 1, nN, 1  n  5}

TYPES OF SETS Null set or empty set : A set having no element in it is called an empty set or a null set or void set, it is denoted by  or { }. A set consisting of at least one element is called a non-empty set or a non-void set. Singleton set : A set consisting of a single element is called a singleton set. Finite set : A set which has only finite number of elements is called a finite set. Order of a finite set : The number of elements in a finite set A is called the order of this set and denoted by O(A) or n(A). It is also called cardinal number of the set. e.g. A = {a, b, c, d}  n(A) = 4 Infinite set : A set which has an infinite number of elements is called an infinite set. Equal sets : Two sets A and B are said to be equal if every element of A is member of B, and every element of B is a member of A. If sets A and B are equal, we write A = B and if A and B are not equal then A  B Equivalent sets : Two finite sets A and B are equivalent if their number of elements are same i.e. n(A) = n(B) e.g. 

A = {1, 3, 5, 7}, B = {a, b, c, d} A and B are equivalent sets

RESONANCE



n(A) = 4 and n(B) = 4

Sets, Relations and Binary Operations - 1

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Note - Equal sets are always equivalent but equivalent sets may not be equal Example # 4 : Identify the type of set : (i) A = {x  N : 5 < x < 6} (ii) A = {a, b, c} (iii) A = {1, 2, 3, 4, .......} (iv) A = {1, 2, 6, 7} and B = {6, 1, 2, 7, 7} (v) A = {0} Solution : (i) Null set (ii) finite set (iii) infinite set (iv) equal sets (v) singleton set Self Practice Problem : (1) Write the set of all integers 'x' such that |x – 3| < 8. (2) Write the set {1, 2, 3, 6} in set builder form. (3) If A = {x : |x| < 2, x  Z} and B = {–1, 1} then find whether sets A and B are equal or not. Answers

(1) (2) (3)

[–4, –3, –2, –1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] {x : x is a natural number and a divisor of 6} Not equal sets

SUBSET AND SUPERSET : Let A and B be two sets. If every element of A is an element B then A is called a subset of B and B is called superset of A. We write it as A  B. e.g.

A = {1, 2, 3, 4} and B = {1, 2, 3, 4, 5, 6, 7} If A is not a subset of B then we write A / B



A  B

PROPER SUBSET : If A is a subset of B but A  B then A is a proper subset of B and we write A  B. Set A is not proper subset of A so this is improper subset of A Note : (i)

Every set is a subset of itself

(ii)

Empty set  is a subset of every set

(iii)

A  B and B  A  A = B

(iv) (v) (vi)

The total number of subsets of a finite set containing n elements is 2n. Number of proper subsets of a set having n elements is 2n – 1. Empty set  is proper subset of every set except itself.

POWER SET : Let A be any set. The set of all subsets of A is called power set of A and is denoted by P(A) Example # 5 : Examine whether the following statements are true or false : (i) {a, b} / {b, c, a} (ii) (iii) (iv) Solution :

{a, e} / {x : x is a vowel in the English alphabet} {1, 2, 3}  {1, 3, 5}

{a} {a, b, c} (i) False as {a, b} is subset of {b, c, a} (ii) True as a, e are vowels (iii) False as element 2 is not in the set {1, 3, 5} (iv) False as a {a, b, c} and {a}  {a, b, c} RESONANCE Sets, Relations and Binary Operations - 2

CCXIIISEET

Example # 6 : Find power set of set A = {1, 2} Solution : P(A) = {, {1}, {2}, {1, 2}} Example # 7 : If  denotes null set then find P(P(P())) Solution : Let P() = {} P(P()) = {,{}} P(P(P())) = {, {}, {{}}, {, {}}} Self Practice Problem : (4) State true/false :A = {1, 3, 4, 5}, B = {1, 3, 5} then A  B. (5)

State true/false :A = {1, 3, 7, 5}, B = {1, 3, 5, 7} then A  B.

(6)

State true/false :[3, 7]  (2, 10)

Answers

(4)

False

(5)

False

(6)

True

UNIVERSAL SET : A set consisting of all possible elements which occur in the discussion is called a universal set and is denoted by U. e.g. if A = {1, 2, 3}, B = {2, 4, 5, 6}, C = {1, 3, 5, 7} then U = {1, 2, 3, 4, 5, 6, 7} can be taken as the universal set.

SOME OPERATION ON SETS : (i) Union of two sets : A  B = {x : x  A or x  B} e.g. A = {1, 2, 3}, B = {2, 3, 4} then A  B = {1, 2, 3, 4} (ii) Intersection of two sets : A  B = {x : x  A and x  B} e.g. A = {1, 2, 3}, B = {2, 3, 4} then A  B = {2, 3} (iii) Difference of two sets : A – B = {x : x  A and x  B}. It is also written as AB'. Similarly B – A = B  A' e.g. A = {1, 2, 3}, B = {2, 3, 4} ; A – B = {1} (iv) Symmetric difference of sets : It is denoted by A  B and A  B = (A – B)  (B – A) (v) Complement of a set : A' = {x : x  A but x  U} = U – A e.g. U = {1, 2,........, 10}, A = {1, 2, 3, 4, 5} then A' = {6, 7, 8, 9, 10} (vi) Disjoint sets : If A  B = , then A, B are disjoint e.g. If A = {1, 2, 3}, B = {7, 8, 9} then A  B = 

VENN DIAGRAM : Most of the relationships between sets can be represented by means of diagrams which are known as venn diagrams.These diagrams consist of a rectangle for universal set and circles in the rectangle for subsets of universal set. The elements of the sets are written in respective circles. For example If A = {1, 2, 3}, B = {3, 4, 5}, U = {1, 2, 3, 4, 5, 6, 7, 8} then their venn diagram is

RESONANCE

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AB

A'

AB

A–B

(A B) = (A – B)  (B – A)

B–A

Disjoint

LAWS OF ALGEBRA OF SETS (PROPERTIES OF SETS): (i) Commutative law : (A  B) = B  A ; A  B = B  A (ii) Associative law : (A  B)  C = A  (B  C) ; (A  B)  C = A  (B  C) (iii) Distributive law : A (B  C) = (A  B)  (A  C) ; A  (B  C) = (A  B)  (A  C) (iv) De-morgan law : (A  B)' = A'  B' ; (A  B)' = A'  B' (v) Identity law : A  U = A ; A   = A (vi) Complement law : A  A' = U, A  A' = , (A')' = A (vii) Idempotent law : A  A = A, A  A = A NOTE : (i) A – (B  C) = (A – B)  (A – C) ; A – (B  C) = (A – B)  (A – C) (ii) A   = , A  U = U Example # 8 : Let A = {2, 4, 6, 8} and B = {6, 8, 10, 12} then find A  B Solution : A  B = {2, 4, 6, 8, 10, 12} Example # 9 : Let A = {1, 2, 3, 4, 5, 6}, B = {2, 4, 6, 8}. Find A – B and B – A. Solution :

A – B = {x : x  A and x  B} = {1, 3, 5} similarly B – A = {8}

Example # 10 : State true or false : (i) A  A =  (ii)  A = A Solution : (i) false because A  A' = U (ii) true as  A = U A = A Example # 11 : Use Venn diagram to prove that A  B  B  A.

Solution :

From venn diagram we can conclude that B  A. Example # 12 Solution : Now    

: Prove that if A  B = C and A  B =  then A = C – B. Let x A xAB xC ( AB = C) AB =  xB ( x  A) x C – B ( x  C and x  B) AC–B Let xC–B  x  C and x  B xAB and x  B xA  C – B A A=C–B

RESONANCE

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Self Practice Problem : (7) Find A  B if A = {x : x = 2n + 1, n  5, n  N} and B = {x : x = 3n – 2, n  4, n  N}. (8)

Find A – (A – B) if A = {5, 9, 13, 17, 21} and B = {3, 6, 9, 12, 15, 18, 21, 24}

Answers

(7)

{1, 3, 4, 5, 7, 9, 10, 11}

(8)

{9, 21}

SOME IMPORTANT RESULTS ON NUMBER OF ELEMENTS IN SETS : If A, B, C are finite sets and U be the finite universal set then (i)

n(A  B) = n(A) + n(B) – n(A  B)

(iii)

n(A – B) = n(A) – n(A  B)

(v)

n(A  B  C) = n(A) + n(B) + n(C) – n(A  B) – n(B  C) – n(A  C) + n(A  B  C)

(vi)

Number of elements in exactly two of the sets A, B, C = n(A  B) + n(B  C) + n(C  A) – 3n(A  B  C)

(vii)

Number of elements in exactly one of the sets A, B, C = n(A) + n(B) + n(C) – 2n(A  B) – 2n(A  B) – 2n(B  C) – 2n(A  C) + 3n(A  B  C)

Example # 13 : In a group of 40 students, 26 take tea, 18 take coffee and 8 take neither of the two. How many take both tea and coffee ? Solution n(U) = 40, n(T) = 26, n(C) = 18 n(T  C) = 8  n(T  C) = 8  n(U) – n(T  C) = 8  n(T  C) = 32  n(T) + n(C) – n(T  C) = 32  n(T  C) = 12 Example # 14 : In a group of 50 persons, 14 drink tea but not coffee and 30 drink tea. Find (i) How many drink tea and coffee both ? (ii) How many drink coffee but not tea ? Solution T : people drinking tea C : people drinking coffee (i) n(T) = n(T – C) + n(T  C)  30 = 14 + n(T  C)  n(T  C) = 16

(ii) n(C – T) = n(T  C) – n(T) = 50 – 30 = 20 Self Practice Problem : (9) Let A and B be two finite sets such that n(A – B) = 15, n(A  B) = 90, n(A  B) = 30. Find n(B) (10)

A market research group conducted a survey of 1000 consumers and reported that 720 consumers liked product A and 450 consumers liked product B. What is the least number that must have liked both products ?

Answers

(9)

RESONANCE

75

(10)

170

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RELATIONS ORDERED PAIR : A pair of objects listed in a specific order is called an ordered pair. It is written by listing the two objects in specific order separating them by a comma abd enclosing the pair in parantheses. In the ordered pair (a, b), a is called the first element and b is called the second element. Two ordered pairs are set to be equal if their corresponding elements are equal. i.e. (a, b) = (c, d) if a = c and b = d.

CARTESIAN PRODUCT : The set of all possible ordered pairs (a, b), where a  A and b  B i.e. {(a, b) ; a  A and b  B} is called the cartesian product of A to B and is denoted by A × B. Usually A × B  B × A. Similarly A × B × C = {(a, b, c) : a  A, b  B, c  C} is called ordered triplet.

RELATION: Let A and B be two sets. Then a relation R from A to B is a subset of A × B. Thus, R is a relation from A to B  R  A × B. The subsets is derived by describing a relationship between the first element and the second element of ordered pairs in A × B e.g. if A = {1, 2, 3, 4, 5, 6, 7, 8} and B = {1, 2, 3, 4, 5} and R = {(a, b) : a = b2, a  A, b  B} then R = {(1, 1), (4, 2), (9, 3)}. Here a R b  1 R 1, 4 R 2, 9 R 3.

NOTE : (i)

(ii)

Let A and B be two non-empty finite sets consisting of m and n elements respectively. Then A × B consists of mn ordered pairs. So total number of subsets of A × B i.e. number of relations from A to B is 2mn. A relation R from A to A is called a relation on A.

DOMAIN AND RANGE OF A RELATION : Let R be a relation from a set A to a set B. Then the set of all first components of coordinates of the ordered pairs belonging to R is called to domain of R, while the set of all second components of corrdinates of the ordered pairs in R is called the range of R. Thus, Dom (R) = {a : (a, b)  R} and Range (R) = {b : (a, b)  R} It is evident from the definition that the domain of a relation from A to B is a subset of A and its range is a subset of B. Example # 1 : If A = {1, 2} and B = {3, 4}, then find A × B. Solution : A × B = {(1, 3), (1, 4), (2, 3), (2, 4)} Example # 2 : Let A = {1, 3, 5, 7} and B = {2, 4, 6, 8} be two sets and let R be a relation from A to B defined by the phrase "(x, y)  R  x > y". Find relation R and its domain and range. Solution : Under relation R, we have 3R2, 5R2, 5R4, 7R4 and 7R6 i.e. R = {(3, 2), (5, 2), (5, 4), (7, 2), (7, 4), (7, 6)}  Dom (R) = {3, 5, 7} and range (R) = {2, 4, 6} Example # 3 : Let A = {2, 3, 4, 5, 6, 7, 8, 9}. Let R be the relation on A defined by {(x, y) : x  A, y  A and x divides y}. Find domain and range of R. Solution: The relation R is R = {(2, 2), (2, 4), (2, 6), (2, 8), (3, 3), (3, 6), (3, 9), (4, 4), (4, 8), (5, 5), (6, 6), (7, 7), (8, 8), (9, 9)} Domain of R = {2, 3, 4, 5, 6, 7, 8, 9} = A Range of R = {2, 3, 4, 5, 6, 7, 8, 9} = A

RESONANCE

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CCXIIISEET

Self Practice Problem : (1) If (2x + y, 7) = (5, y – 3) then find x and y. (2)

If A × B = {(1, 2), (1, 3), (1, 6), (7, 2), (7, 3), (7, 6)} then find sets A and B.

(3)

If A = {x, y, z} and B = {1, 2} then find number of relations from A to B.

(4)

Write R = {(4x + 3, 1 – x) : x  2, x  N}

Answers

(1) x = – (3) 64

5 , y = 10 2

(2) A = {1, 7}, B = {2, 3, 6} (4) {(7, 0), (11, –1)}

TYPES OF RELATIONS : In this section we intend to define various types of relations on a given set A. (i)

Void relation : Let A be a set. Then   A × A and so it is a relation on A. This relation is called the void or empty relation on A.

(ii)

Universal relation : Let A be a set. Then A × A  A × A and so it is a relation on A. This relation is called the universal relation on A.

(iii)

Identity relation : Let A be a set. Then the relation IA = {(a, a) : a  A} on A is called the identity relation on A. In other words, a relation IA on A is called the identity relation if every element of A is related to itself only.

(iv)

Reflexive relation : A relation R on a set A is said to be reflexive if every element of A is related to itself. Thus, R on a set A is not reflexive if there exists an element a  A such that (a, a)  R.

(v)

Note : Every identity relation is reflexive but every reflexive relation in not identity. Symmetric relation : A relation R on a set A is said to be a symmetric relation iff (a, b)  R  (b ,a)  R for all a, b  A. i.e. a R b  b R a for all a, b  A.

(vi)

Transitive relation : Let A be any set. A relation R on A is said to be a transitive relation iff (a, b)  R and (b, c)  R  (a, c)  R for all a, b, c  A i.e. a R b and b R c  a R c for all a, b, c  A

(vii)

Equivalence relation : A relation R on a set A is said to be an equivalence relation on A iff (i) it is reflexive i.e. (a, a)  R for all a  A (ii) it is symmetric i.e. (a, b)  R  (b, a)  R for all a, b  A (iii) it is transitive i.e. (a, b)  R and (b, c)  R  (a, c)  R for all a, b  A

Example # 4 : Which of the following are identity relations on set A = {1, 2, 3}. R1 = {(1, 1), (2, 2)}, R2 = {(1, 1), (2, 2), (3, 3), (1, 3)}, R3 = {(1, 1), (2, 2), (3, 3)}. Solution: The relation R3 is idenity relation on set A. R1 is not identity relation on set A as (3, 3)  R1. R2 is not identity relation on set A as (1, 3)  R2 Example # 5 : Which of the following are reflexive relations on set A = {1, 2, 3}. R1 = {(1, 1), (2, 2), (3, 3), (1, 3), (2, 1)}, R2 = {(1, 1), (3, 3), (2, 1), (3, 2)}.. Solution : R1 is a reflexive relation on set A. R2 is not a reflexive relation on A because 2  A but (2, 2)  R2. Example # 6 : Prove that on the set N of natural numbers, the relation R defined by x R y  x is less than y is transitive. Solution : Because for any x, y, z  N x < y and y < z  x < z  x R y and y R z  x R z. so R is transitive.

RESONANCE

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Example # 7 : Let T be the set of all triangles in a plane with R a relation in T given by R = {(T1 , T2) : T1 is congruent to T2}. Show that R is an equivalence relation. Solution : Since a relation R in T is said to be an equivalenece relation if R is reflexive, symmetric and transitive. (i) Since every triangle is congruent to itself  R is reflexive (ii) (T1 , T2)  R  T1 is congruent to T2  T2 is congruent to T1  (T2, T1)  R Hence R is symmetric (iii) Let (T1, T2)  R and (T2, T3)  R  T1 is congruent to T2 and T2 is congruent to T3  T1 is congruent to T3  (T1, T3)  R  R is transitive Hence R is an equivalence relation. Example # 8 : Show that the relation R in R defined as R = {(a, b) : a  b} is transitive. Solution : Let (a, b)  R and (b, c)  R  (a  b) and b  c  a  c  (a, c)  R Hence R is transitive. Example # 9 : Show that the relation R in the set {1, 2, 3} given by R = {(1, 2), (2, 1)} is symmetric. Solution : Let (a, b)  R [ (1, 2)  R]  (b, a)  R [ (2, 1)  R] Hence R is symmetric. Self Practice Problem : (5) Let L be the set of all lines in a plane and let R be a relation defined on L by the rule (x ,y)  R  x is perpendicular to y. Then prove that R is a symmetric relation on L. (6)

Let R be a relation on the set of all lines in a plane defined by (1, 2)  R  line 1 is parallel to line 2. Prove that R is an equivalence relation.

BINARY OPERATIONS BINARY OPERATION A binary operation * on a set A is a function * : A × A  A. We denote * (a, b) by a * b. Example # 1 : Show that addition, subtraction and multiplication are binary operations on R, but division is not a binary operation on R. Further, show that division is a binary operation on the set R* of non zero real numbers. Solution : + : R × R  R is given by (a, b)  a + b – : R × R  R is given by (a, b)  a – b × : R × R  R is given by (a, b)  ab Since ‘+’, ‘–’ and ‘×’ are functions, they are binary operations on R. But  : R × R  R, given by (a, b)  b = 0,

a , is not a function and hence not a binary operation, as for b

a is not defined. b

However  : R* × R*  R*, given by (a, b) 

RESONANCE

a is a function and hence a binary operation on R*. b

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Example # 2 : Show that subtraction and division are not binary operations on N. Solution : – : N × N  N, given by (a, b)  a – b is not binary operation as the image of (3, 5) under ‘–’ is 3 – 5 = –2   N. Similarly  : N × N  N given by (a, b)  a  b is not a binary operation as the image of (3, 5) under  is 3  5 =

3   N. 5

Example # 3 : Show that * : R × R  R given by (a, b)  a + 4b2 is a binary operation. Solution : Since * carries each pair (a, b) to a unique element a + 4b2 in R, * is a binary operation on R. Example # 4 : Show that the  : R × R  given by (a, b)  max {a, b} and  : R × R  R given by (a, b)  min {a, b} are binary operations. Solution : Since  carries each pair (a, b) in R × R to a unique element namely maximum of a and b lying in R,  is a binary operation. Using the similar argument, one can say that  is also a binary operation.

OPERATION TABLE When number of elements in a set A is small, we can express a binary operation * on the set A through a table called the operation table for the operation *. For example consider A = {1, 2, 3}. Then the operation * on A defined as * : R × R  given by (a, b)  max {a, b} can be expressed by the following operation table. Here *(1, 3) = 3, *(2, 3) = 3, *(1, 2) = 2.

*

1 2 3

1 1 2 3 2 2 2 3 3 3 3 3

LAWS OF BINARY OPERATIONS : (i) Commutative Law : A binary operation * on the set X is called commutative if a * b = b * a for every a, b  X. (ii) Associative Law : A binary operation * : A × A  A is said to be associative if (a * b) * c = a * (b * c)  a, b, c  A. Example # 5 : : Show that + : R × R  R and × : R × R  R are commutative binary operations but – : R × R  R and  : R × R  R are not commutative. Solution : Since a + b = b + a and a × b = b × a  a b  R so '+' and '×' are commutative binary operations. However '–' is not commutative since 3 – 4  4 – 3. Similarly 3  4  4  3 shows that  is not commutative. Example # 6 : Show that * : R × R  R defined by a * b = a + 2b is not commutative. Solution : Since 3 * 4 = 3 + 8 = 11 and 4 * 3 = 4 + 6 = 10, showing that the operation * is not commutative. Example # 7 : Show that addition and multiplication are associative binary operations on R. But subtraction is not associative on R. Division is not associative on R. Solution : Addition and multiplication are associative since (a + b) + c = a + (b + c) and (a × b) × c = a × (b × c)  a, b, c  R. However subtraction and division are not associative as (8 – 5) – 3  8 – (5 – 3) and (8  5) 3  8  (5  3). Example # 8 : Show that * : R × R  R given by a * b  a + 2b is not associative. Solution : The operation * is not associative since (8 * 5) * 3 = (8 + 10) * 3 = (8 + 10) + 6 = 24. while 8 * (5 * 3) = 8 * (5 + 6) = 8 * 11 = 8 + 22 = 30. Self Practice Problem : (1) Find whether the operation * on Z defined by a * b = ab is binary or not. (2)

Let * be a binary operation on Q. Find 2 * 3 if a * b = 3a – 5b

RESONANCE

Sets, Relations and Binary Operations - 9

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(3) Show that the binary operations * on Q defined by a * b = a + 12b + ab is not associative. Answers (1) No (2) –9

EXISTENCE OF IDENTITY ELEMENT : Given a binary operation * : A × A  A an element e  A if it exists is called identity for the operation * if a * e = a = e * a  a  A. Example # 9 : Show that zero is the identity for addition on R but 1 is the identity for multiplicaton on R. But there is no identity element for the operations – : R × R  R and  : R* × R*  R*. Solution. a + 0 = 0 + a = a and a × 1 = a = 1 × a  a  R implies that 0 and 1 are identity elements for the operations '+' and '×' respectively. Further there is no element e in R with a – e = e – a  a. Similarly we can not find any element e in R* such tht a  e = e  a  a in R*. Hence, '–' and '' do not have identity element.

EXISTENCE OF INVERSE : Given a binary operation * : A × A  A with the identity element e in A, an element a  A is said to be invertible with respect to the operation * if there exists an element b in A such that a * b = e = b * a and b is called the inverse of a and is denoted by a–1. Remark :Zero is identity for the addition operation on R but it is not identity for the addition operation on N as 0   N. In fact the addition operation on N does not have any identity. One further notices that for the addition operation + : R × R  R, given any a  R, there exists – a in R such that a + (–a) = 0 (identity for '+') = (–a) + a. Similarly for the multiplication operation on R given any a  0 in R, we can choose 1/a in R such that a × 1/a = 1(identity for '×') = 1/a × a. This leads to the existence of inverse. Example # 10 : Show that –a is the inverse of a for the addition operation '+' on R and 1/a is the inverse of a  0 for the multiplication operation '×' on R. Solution : As a + (–a) = a – a = 0 and (–a) + a = 0, –a is the inverse of a for addition. Similarly for a  0 a ×

1 1 1 =1= × a implies that is the inverse of a for multiplication. a a a

Example # 11 : Show that –a is not the inverse of a  N for the addition operation + on N and Solution :

1 is not the inverse a

of a  N for multiplication operation × on N for a  1. Since –a   N, –a can not be inverse of a for addition operation on N. Althrough –a satisfies a + (–a) = 0 = (–a) + a. 1   N which implies that other than 1, no element of N has inverse for a multiplication operation on N.

Similarly for a  1 in N,

Self Practice Problem : (4) Let * be a binary operation 'addition' on set of integers find the identity element of (Z, *). (5) Consider the binary operations * Q × Q  Q defind by a * b = a + b + ab ; a, b  Q. Find inverse of rational number 5. Answers (4) 0 (5) – 5/6

RESONANCE

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OBJECTIVE QUESTIONS * Marked Questions are having more than one correct option. SECTION (A) : Representation of set, Types of sets, Subset, Power Set. A-1.

A-2.

Which of the following is the empty set (A) {x : x is a real number and x2 – 1 = 0}

(B) {x : x is a real number and x2 + 1 = 0}

(C) {x : x is a real number and x2 – 9 = 0}

(D) {x : x is a real number and x2 = x + 2}

The set A = {x : x R, x2 = 16 and 2x = 6} is (A) Null set

A-3.

(B) Singleton set

(D) None of these

If A = {x :|x| < 3, x  Z} then the number of subsets of A is (A) 120

A-4.

(C) Infinite set

(B) 30

(C) 31

The number of subsets of the power set of set A = {7, 10, 11} is (A) 32 (B) 16 (C) 64

(D) 32

(D) 256

SECTION (B) : Venn diagrams, Algebra of sets. B-1.

Sets A and B have 3 and 6 elements respectively. What can be the minimum number of elements in AB ? (A) 3 (B) 6 (C) 9 (D) 18

B-2.

If the sets A and B are defined as A = {(x, y) : y =

1 , x  R, x  0} x

B = {(x, y) : y = – x, x  R}, then (A) A B = A B-3.

(C) {x : 1  x  2}

(D) None of these

(B) A  B  A  B

(C) A  B = A  B

(D) None of these

(B) A  (B  C)

(C) A  (B – C)

(D) A – (B  C)

Let n(U) = 700, n(A) = 200, n(B) = 300 and n(A  B) = 100, then n(A'  B') = (A) 400

B-7.

(B) {x : 1  x < 2}

The shaded region in the given figure is

(A) A  (B  C) B-6.

(D) None of these

Let A and B be two sets. Then (A) A  B  A  B

B-5.

(C) A  B = 

Let A = {x : x  R, |x| < 1} : B = {x : x  R, |x – 1|  1} and A B = R – D, then the set D is (A) {x : 1 < x  2}

B-4.

(B) A  B = B

(B) 600

(C) 300

(D) 200

If X = {4n – 3n – 1 : n  N} and Y = {9(n – 1) ; n  N}, then X Y is equal to (A) X

RESONANCE

(B) Y

(C) N

(D) None of these

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SECTION (C) : Theorems on cardinal number C-1.

In a college of 300 students, every student reads 5 newspapers and every newspaper is read by 60 students. The number of newspaper is(A) at least 30 (B) at most 20 (C) exactly 25 (D) none of these

C-2.

In a town of 10,000 families it was found that 40% families buy newspaper A, 20% families buy newspaper B and 10% families buy newspaper C, 5% families buy A and B, 3 % buy B and C and 4% buy A and C. If 2% families buy all the three news papers, then number of families which buy newspaper A only is (A) 3100

C-3.

(B) 3300

(C) 2900

(D) 1400

In a city 20 percent of the population travels by car, 50 percent travels by bus and 10 percent travels by both car and bus. Then persons travelling by car or bus is (A) 80 percent (B) 40 percent (C) 60 percent (D) 70 percent

SECTION (D) : Cartesian Product of sets, Domain, range and co-domain of Relation. D-1.

If A = {2, 4, 5}, B = {7, 8, 9}, then n(A × B) is equal to (A) 6

D-2.

(C) 3

(D) 0

If A = {x : x2 – 5x + 6 = 0}, B = {2, 4}, C = {4, 5} then A × (B  C) is(A) {(2, 4), (3, 4)}

D-3.

(B) 9

(B) {(4, 2), (4, 3)}

(C) {(2, 4), (3, 4), (4, 4)} (D) {(2, 2), (3, 3), (4, 4), (5, 5)}

A and B are two sets having 3 and 4 elements respectively and having 2 elements in common. The number of relation which can be defined from A to B is (A) 25

(B) 210 – 1

(C) 212 – 1

(D) none of these

SECTION (E) : Types of Relations E-1.

Let A = {1, 2, 3, 4} and R be a relation in A given by R = {(1, 1), (2, 2), (3, 3), (4, 4), (1, 2), (2, 1), (3, 1), (1, 3)}, then relation R is (A) Reflexive (B) Symmetric (C) Equivalence (D) Reflexive and Symmetric

E-2.

The relation R = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 3), (1, 3)} on set A = {1, 2, 3} is

E-3.

(A) Reflexive but not symmetric

(B) Reflexive but not transitive

(C) Symmetric and Transitive

(D) Neither symmetric nor transitive

The relation ''less than'' in the set of natural number is (A) Only symmetric

E-4.

E-5.

(D) Equivalence relation

(A) Reflexive but not symmetric

(B) Symmetric but not transitive

(C) Symmetric and transitive

(D) None of these

In the set A = {1, 2, 3, 4, 5}, a relation R is defined by R = {(x, y)| x, y  A and x < y}. Then R is (B) Symmetric

(C) Transitive

(D) None of these

For real numbers x and y, we write x R y  x – y + 2 is an irrational number. Then the relation R is(A) Reflexive

E-7.

(C) Only reflexive

The relation R defined in N as aRb b is divisible by a is

(A) Reflexive

E-6.

(B) Only transitive

(B) Symmetric

(C) Transitive

(D) None of these

Which one of the following relations on R is equivalence relation(A) x R1y  |x| = |y|

RESONANCE

(B) x R2y  x  y

(C) x R3y  x | y

(D) x R4y  x < y

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E-8.

E-9.

The relation R defined in A = {1, 2, 3} by a R b if |a2 – b2|  5. Which of the following is false(A) R = {(1, 2), (2, 2), (3, 3), (2, 1), (2, 3), (3, 2)

(B) Co-domain of R = {1, 2, 3}

(C) Domain of R = {1, 2, 3}

(D) Range of R = {1, 2, 3}

Let P = {(x, y) | x2 + y2 = 1, x, y  R}, then P is (A) reflexive

(B) symmetric

(C) transitive

(D) anti-symmetric

E-10.

Let A = {p, q , r}. Which of the following is an equivalence relation on A ? (A) R1 = {(p, q), (q, r), (p, r) (p, p)} (B) R2 = {(r, q), (r, p), (r, r) (q, q)} (C) R3 = {(p, p), (q, q), (r, r) (p, q)} (D) none of these

E-11.

Let R1 be a relation defined by R1 = {(a, b)| a  b ; a, b  R} . Then R1 is (A) An equivalence relation on R (B) Reflexive, transitive but not symmetric (C) Symmetric, Transitive but not reflexive (D) Neither transitive nor reflexive but symmetric

E-12.

Let L denote the set of all straight lines in a plane. Let a relation R be defined by R ,, L. The R is (A) Reflexive (B) Symmetric (C) Transitive (D) None of these

E-13.

Let S be the set of all real numbers. Then the relation R = {(a, b) : 1 + ab > 0} on S is (A) Reflexive and symmetric but not transitive (B) Reflexive, transitive but not symmetric (C) Symmetric, transitive but not reflexive (D) Reflexive, transitive and symmetric

E-14.

Let R be a relation on the set N be defined by {(x, y)| x, y  N, 2x + y = 41}. Then R is (A) Reflexive (B) Symmetric (C) Transitive (D) None of these

SECTION (F) : Binary Operation F-1.

Let A = {1, 2, 3, 4, 5, 6} and * be an operation A defined by a * b = r, where r is the least non-negative remainder when the product ab is divided by k. Operation * is binary operation if k = (A) 7 (B) 11 (C) 21 (D) 17

F-2

Let * be a binary operation on Z .If a * b = (a2 + b3)2 where a, b  Z then the value of 5 * 3 is (A) 1256 (B) 2704 (C) 64 (D) 34

F-3.

Let * be a binary operation on Z .If a * b = 2ab where a, b  Z then the value of 19 * 16 is (A) 608 (B) 70 (C) 68 (D) 304

F-4.

Let * be a binary operation on Z defined by x * y = x2 + y2 + xy; x, y  Z. The value of [(1 * 2) + (0 * 3)]2 is (A) 16 (B) 19 (C) 361 (D) 256

F-5.

Let * be a binary operation on N defined by a * b = 25ab ; a, b  N. then the binary operation * is (A) Only commutative (B) Only associative (C) Both commutative and associative (D) Neither commutative nor associative

F-6.

Let * be a binary operation on Z defined by a * b = a + b – 15 for a, b  Z. The identity element in (Z, ) is (A) 5 (B) 10 (C) 15 (D) 0

F-7.

Let * be a binary operation on Z defined by a * b = a + b – 15 for a, b  Z. The inverse of element 21 in (Z, ) is (A) 12 (B) –21 (C) 9 (D) 1/21

COMPREHENSIONS Comprehension # 1 Let R be a relation defined as R = { (x y) : y = |x – 1|, x  Z and | x |  3} 1. Relation R is equal to : (A) {(1, 0), (1, 2), (3, 2), (4, 3)} (B) {(–3, 4), (–2, 3), (–1, 2), (0, 1), (1, 0), (2, 1), (3, 2)} (C) {(4, –3), (3, –2), (2 –1), (1, 0), (2, 3)} (D) None of these 2.

Domain of R is : (A) {0, 1, 2, 3, 4} (C) {– 3, – 2, – 1, 0, 1, 2, 3}

RESONANCE

(B) {1, 3, 4} (D) {0, 1, 2, 3, 4} Sets,Relations and Binary Operations - 13

CCXIIISEET

3.

Range of R is (A) {0, 1, 2, 3, 4} (C) {–4, –3, –1, –2, 0}

(B) {–3, –2, –1, 0, 1, 2, 3} (D) {–1, 0, 1, 2, 3, 4}

SUBJECTIVE QUESTIONS 1.

Write the set of all vowels in English alphabet which precede letter O.

2.

Describe the following set by set property method {0, 3, 8, 15, 24, 35}

3.

Which of the following are true ? (i) If A = {1, 5, 5, 5}, B = {1, 3, 5}, then A  B. (ii) If A = {x : x3 – 1 = 0, x  N}, B = {x : x2 – 4x + 3 = 0, x  N} then A  B.

4.

Assume that P(A) = P(B). Prove that A = B.

5.

If A = {x : x = 4n + 1, n  5, n  N} and B {3n : n  8, n  N}, then find A – (A – B).

6.

Prove that A  B = A  B iff A = B.

7.

Prove that : A – (B  C) = (A – B)  (A – C) without using venn diagram.

8.

Prove by using venn diagram (i) A – (B  C) = (A – B)  (A – C)

9.

(ii) A  B  B  A

Which of the following venn-diagrams best represents the sets of females, mothers and doctors ?

(A)

(B)

(C)

(D)

10.

Of the members of three athletic teams in a school 21 are in the cricket team, 26 are in the hockey team and 29 are in the football team. Among them, 14 play hockey and cricket, 15 play hockey and football, and 12 play football and cricket. Eight play all the three games. Find the total number of members in the three athletic teams.

11.

In a class of 55 students, the number of students studying different subjects are 23 in Mathematics, 24 in Physics, 19 in Chemistry, 12 in Mathematics and Physics 9 in Mathematics and Chemistry, 7 in Physics and Chemistry and 4 in all the three subjects. Find the number of students who have taken exactly one subject.

12.

Determine the domain and the range of the relation R defined by R = {(x + 1, x + 5) : x  {0, 1, 2, 3, 4, 5}}.

13.

If A = {3, 4, 6}, B = {1, 3} and C = {1, 2, 6} then find (A – B) × (A – C).

14.

Let n be a fixed positive integer. Define a relation R on the set of integers Z, aRb n|(a – b). Then prove that R is equivalence relation

15.

Let R be a relation over the set N × N and it is defined by (a, b) R (c, d)  a + d = b + c. Then prove that R is equivalence relation

RESONANCE

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16.

Let L be the set of all straight lines in the Euclidean plane. Two lines 1 and 2 are said to be related by the relation R if 1 is parallel to 2. Then prove that R is equivalence relation.

17.

For n, m  N, n | m means that n is a factor of m, then prove that relation | is reflexive, transitive but not symmetric.

18.

Let R = {(x, y) : x, y  A, x + y = 5} where A = {1, 2, 3, 4, 5} then prove that R is neither reflexive nor transitive but symmetric.

19.

Let * be a binary operation on the set R defined by a * b = a + b + ab, a, b  R. Solve the equation 2 * (3 * x) = 7

20.

Let * be a binary operation on Z × Z defined by (a, b) * (c, d) = (a + c, b + d); (a, b), (c, d)  Z × Z. Find (1, 2) * (3, 5) and (4, 3) * (1, 0).

21.

Consider the binary operation * on Q defined by a * b = a + 12b + ab for a, b  Q. Show that * is not commutative.

22.

Let A = N × N and '*' be a binary operation on A defined by (a, b) * (c, d) = (ad + bc, bd). Show that (A, ) has no identity element.

23.

If  is a binary operation on R defined by a  b =

a b + for a, b  R, then show that : 4 7

(2  5)  7  2  (5  7). 24.

Let A = {1, –1, i, –i}, where i = on A.

25.

Does the composition table :

 1 . Draw the composition table corresponding to binary operation 'multiplication'

* a b c a b c a b c a b c a b c

give a commutative binary operation on the set {a, b, c} ?

AIEEE PROBLEMS (PREVIOUS YEARS) 1.

If A, B and C are three sets such that A  B = A C and A  B = A C, then (1) A = C

2.

(3) A  B = 

(4) A = B

Let R = {(1, 3), (4, 2), (2, 4), (2, 3), (3, 1)} be a relation on the set A = {1, 2, 3, 4}. The relation R is[AIEEE - 2004] (1) transitive

3.

(2) B = C

[AIEEE - 2009]

(2) not symmetric

(3) reflexive

(4) a function

Let R = {(3, 3), (6, 6), (9, 9), (12, 12) (6, 12), (3, 9), (3, 12), (3, 6)} be relation on the set A = {3, 6, 9, 12}. Then the relation R is [AIEEE - 2005] (1) reflexive and transitive only

(2) reflexive only

(3) an equilvalence relation

(4) reflexive and symmetric only

RESONANCE

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4.

5.

Let W denote the words in the english dictionary. Define the relation R by : R = {(x, y)  W × W | the words x and y have at least one letter in common}. Then R is[AIEEE - 2006] (1) reflexive, symmetric and not transitive

(2) reflexive, symmetric and transitive

(3) reflexive, not symmetric and transitive

(4) not reflexive, symmetric and transitive

Let R be the real line. Consider the following subsets of the plane R × R

[AIEEE - 2008]

S = {(x, y) : y = x + 1 and 0 < x < 2} T = {(x, y) : x – y is an integer} Which one of the following is true ? (1) T is an equivalence relation on R but S is not (2) Neither S nor T is an equivalence relation on R (3) Both S and T are equivalence relations on R 6.

(4) S is an equivalence relation on R but T is not

Consider the following relations : R : {(x, y)| x ,y are real numbers and x = wy for some rational number w}

[AIEEE - 2010]

m p S = {  ,  | m, n, p and q are integers such that n, q  0 and qm = pn}, then  n q (1) neither R nor S is an equivalence relation (2) S is an equivalence relation but R is not an equivalence relation (3) R and S both are equivalence relations (4) R is an equivalence relation but S is not an equivalence relation

7.

Let R be the set of real numbers. [AIEEE - 2011, I] Statement-1 : A = {(x, y)  R × R : y – x is an integer} is an equivalence relation on R. Statement-2 : B = {(x, y)  R × R : x = y for some rational number } is an equivalence relation on R. (1) Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1. (2) Statement-1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1. (3) Statement-1 is true, Statement-2 is false. (4) Statement-1 is false, Statement-2 is true.

8.

Consider the following relation R on the set of real square matrices of order 3. [AIEEE - 2011, II] R = {(A, B)|A = P–1 BP for some invertible matrix P}. Statement -1 : R is equivalence relation. Statement - 2 : For any two invertible 3 × 3 matrices M and N, (MN)–1 = N–1M–1. (1) Statement-1 is true, statement-2 is a correct explanation for statement-1. (2) Statement-1 is true, statement-2 is true; statement-2 is not a correct explanation for statement-1. (3) Statement-1 is true, statement-2 is false. (4) Statement-1 is false, statement-2 is true.

9.

Let X = {1, 2, 3, 4, 5}. The number of different ordered pairs (Y, Z) that can formed such that Y X, Z  X and Y  Z is empty, is : [AIEEE- 2012] (1) 52 (2) 35 (3) 25 (4) 53

RESONANCE

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EXERCISE # 1

EXERCISE # 2 1. {a, e, i}

SECTION (A) : A-1.

B

A-2.

A

A-3.

D

A-4.

D

C C

B-3. B-7.

B B

B-4.

B

SECTION (B) : B-1. B-5.

B D

B-2. B-6.

C

C-2.

B

D-2.

5. {9, 21}

13. {(4, 3), (4, 4), (6, 3), (6, 4)}

9. D

20. (4, 7) , (5, 3)

25. Yes B

C-3.

C

A

D-3.

D

EXERCISE # 3

SECTION (D) : D-1.

3. (i) False (ii) True 10. 43 11. 22

12. Domain = {1, 2, 3, 4, 5, 6}, Range = {5, 6, 7, 8, 9, 10}

SECTION (C) : C-1.

2. {x : x = n2 – 1, n  N, n  6}

1. (2) 2. (2) 3. (1) 4. (1) 5. (1) 6. (2) 7.(3) 8. (2) 9. (2)

SECTION (E) : E-1. E-5. E-9. E-13.

D C B A

E-2. E-6. E-10. E-14.

A A D D

E-3. E-7. E-11.

B A B

E-4. E-8. E-12.

A A B

B C

F-3. F-7.

A C

F-4.

D

SECTION (F) : F-1. F-5.

A A

F-2 F-6.

COMPREHENSIONS 1. B

2. C

3. A

RESONANCE

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SUBJECTIVE QUESTIONS 1.

If A = {(x, y) : x2 + y2 = 25} and B = {(x, y) : x2 + 9y2 = 144} then find n(A  B).

2.

In a battle, 70% of the combatants lost one eye, 80% an ear, 75% an arm, 85% a leg, x% lost all the four limbs. Find the minimum value of x.

3.

A survey shows that 63% of the Americans like cheese whereas 76% like apples. If x% of the Americans like both cheese and apples, find the value of x.

4.

Prove that (A B  C) (A  B C)  C = B C

5.

Let B be a subset of A and let P(A : B) = {S : B  S  A}. If A = {a, b, c, d} and B = {a, b}, then list all the elements of P(A : B).

6.

Prove that the relation R = {(x, y) : x2 = xy} is reflexive and transitive but not symmetric

7.

Consider a relation R defined on set of involutory square matrix of order 2. If A, B are two such matrices then relation R is defined as (A, B)  R  (AB)T = ATBT. Prove that relation R is reflexive and symmetric.

8.

Let A = {a, b}. Find the number of binary operations on A.

9.

Let A be the set of all subsets of a non-empty set S. Show that the binary operation 'union' on A is left distributive over the binary operation 'intersection' on A. Also show that 'intersection' is left distributive over 'union'.

1.

4

2.

10

RESONANCE

3.

x  [39, 63]

5.

{a, b}, {a, b, c}, {a, b, d}, {a, b, c, d}

Sets,Relations and Binary Operations - 18