Explain whny the following binary relation on. 1,2,3} Is not R= {(1,1)(1,2),(1,3),(2,1).(2,2).(3,3)}|

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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### Relations and Equivalence Relations

#### Question:
**2. Explain why the following binary relation on S = {1, 2, 3} is not an equivalence relation on S.**

The relation \( R \) is defined as follows: 
\[ R = \{ (1,1), (1,2), (1,3), (2,1), (2,2), (3,3) \} \]

#### Solution:

To determine why \( R \) is not an equivalence relation on the set \( S = \{1, 2, 3\} \), we must evaluate it with respect to the three properties of equivalence relations:

1. **Reflexivity**:
   - For a relation to be reflexive, every element must be related to itself. Specifically, for all \( x \in S \), the pair \( (x, x) \) must be in \( R \).
   - In this case, the pairs \( (1,1) \), \( (2,2) \), and \( (3,3) \) are present in \( R \), so the relation is reflexive.

2. **Symmetry**:
   - For a relation to be symmetric, if \( (a,b) \in R \), then \( (b,a) \) must also be in \( R \).
   - Here, we see that both \( (1,2) \) and \( (2,1) \) are present, which satisfies the symmetric property for these two pairs. However, \( (1,3) \) is in \( R \) but \( (3,1) \) is not in \( R \). This violates the symmetry requirement.

3. **Transitivity**:
   - For a relation to be transitive, if \( (a,b) \in R \) and \( (b,c) \in R \), then \( (a,c) \) must also be in \( R \).
   - In this set, for example, \( (1, 2) \in R \) and \( (2,1) \in R \) imply that \( (1,1) \in R \), which is true. However, \( (1,2) \in R \) and \( (2,3) \in R \) should imply \( (1,3)
Transcribed Image Text:### Relations and Equivalence Relations #### Question: **2. Explain why the following binary relation on S = {1, 2, 3} is not an equivalence relation on S.** The relation \( R \) is defined as follows: \[ R = \{ (1,1), (1,2), (1,3), (2,1), (2,2), (3,3) \} \] #### Solution: To determine why \( R \) is not an equivalence relation on the set \( S = \{1, 2, 3\} \), we must evaluate it with respect to the three properties of equivalence relations: 1. **Reflexivity**: - For a relation to be reflexive, every element must be related to itself. Specifically, for all \( x \in S \), the pair \( (x, x) \) must be in \( R \). - In this case, the pairs \( (1,1) \), \( (2,2) \), and \( (3,3) \) are present in \( R \), so the relation is reflexive. 2. **Symmetry**: - For a relation to be symmetric, if \( (a,b) \in R \), then \( (b,a) \) must also be in \( R \). - Here, we see that both \( (1,2) \) and \( (2,1) \) are present, which satisfies the symmetric property for these two pairs. However, \( (1,3) \) is in \( R \) but \( (3,1) \) is not in \( R \). This violates the symmetry requirement. 3. **Transitivity**: - For a relation to be transitive, if \( (a,b) \in R \) and \( (b,c) \in R \), then \( (a,c) \) must also be in \( R \). - In this set, for example, \( (1, 2) \in R \) and \( (2,1) \in R \) imply that \( (1,1) \in R \), which is true. However, \( (1,2) \in R \) and \( (2,3) \in R \) should imply \( (1,3)
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