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Questions and Answers
What is the subset of A × A that represents a relation in a set A?
The relation R = {(a, b) : a – b = 10} in the set A = {1, 2, 3, 4} is the universal relation.
False
What is the definition of an empty relation in a set A?
A relation R in a set A is called empty relation, if no element of A is related to any element of A, i.e., R = φ ⊂ A × A.
______ relation R in a set ______ is called universal relation, if each element of ______ is related to every element of _, i.e., R = ______ × ______.
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Which of the following relations is trivial?
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The relation R = {(a, b) : a is sister of b} in the set A of all students of a boys school is the universal relation.
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Match the following relations with their definitions:
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How many ways of representing a relation have been seen in Class XI?
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What is a relation R in a set A called if it is reflexive, symmetric, and transitive?
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A relation R in a set A is reflexive if (a, b) ∈ R, for every a ∈ A.
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What is the condition for a relation R in a set A to be symmetric?
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A relation R in a set A is called transitive if (a1, a2) ∈ R and (a2, a3) ∈ R implies that (a1, ____) ∈ R, for all a1, a2, a3 ∈ A.
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In the relation R = {(T1, T2) : T1 is congruent to T2}, what can be said about the relation R?
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The relation R = {(L1, L2) : L1 is perpendicular to L2} is an equivalence relation.
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Match the following types of relations with their definitions:
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What is the notation for 'a is related to b' in a binary relation R?
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What is a necessary condition for a relation R to be an equivalence relation?
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The relation R = {(a, b) : a ≤ b2} is reflexive.
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What is the difference between a reflexive relation and a symmetric relation?
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A relation R is said to be transitive if (a, b) ∈ R and (b, c) ∈ R, then ______________________.
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Which of the following relations is an equivalence relation?
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The relation R = {(x, y) : x – y is an integer} is transitive.
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Match the following relations with their properties:
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What is the difference between a binary relation and an equivalence relation?
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Study Notes
Types of Relations
- A relation in a set A is a subset of A × A.
- The empty set φ and A × A are two extreme relations.
- Definition 1: A relation R in a set A is called an empty relation if no element of A is related to any element of A, i.e., R = φ ⊂ A × A.
- Definition 2: A relation R in a set A is called a universal relation if each element of A is related to every element of A, i.e., R = A × A.
Representing Relations
- Relations can be represented using the raster method and set builder method.
- Relations can also be expressed using the notation a R b if and only if b = a + 1.
Properties of Relations
- Definition 3: A relation R in a set A is called:
- Reflexive, if (a, a) ∈ R, for every a ∈ A.
- Symmetric, if (a1, a2) ∈ R implies that (a2, a1) ∈ R, for all a1, a2 ∈ A.
- Transitive, if (a1, a2) ∈ R and (a2, a3) ∈ R implies that (a1, a3) ∈ R, for all a1, a2, a3 ∈ A.
Equivalence Relations
- Definition 4: A relation R in a set A is said to be an equivalence relation if R is reflexive, symmetric, and transitive.
- Example: The relation R in the set of all triangles in a plane, given by R = {(T1, T2) : T1 is congruent to T2}, is an equivalence relation.
Examples and Exercises
- Example: The relation R in the set of all students of a boys school, given by R = {(a, b) : a is sister of b}, is the empty relation, and R′ = {(a, b) : the difference between heights of a and b is less than 3 meters} is the universal relation.
- Exercise: Determine whether each of the following relations are reflexive, symmetric, and transitive.
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Description
This chapter covers different types of relations, composition of functions, invertible functions, and binary operations. Learn about the properties and examples of relations and functions.