Math Problem Statement

Let A= {1, 2, 3}and R= {(1, 2), (1, 3), (3, 2)}. Determine R ◦R^−1, Dom(R ◦R^−1) and Ran(R ◦R^−1).

Solution

To solve the problem, we need to carefully analyze the composition RR1R \circ R^{-1}, as well as its domain (Dom(RR1)\text{Dom}(R \circ R^{-1})) and range (Ran(RR1)\text{Ran}(R \circ R^{-1})).


Step 1: Understand R1R^{-1} and RR1R \circ R^{-1}

Given R={(1,2),(1,3),(3,2)}R = \{(1, 2), (1, 3), (3, 2)\}, the inverse relation R1R^{-1} is obtained by swapping the components of each pair in RR: R1={(2,1),(3,1),(2,3)}.R^{-1} = \{(2, 1), (3, 1), (2, 3)\}.

The composition RR1R \circ R^{-1} is defined as: RR1={(a,c)b such that (a,b)R and (b,c)R1}.R \circ R^{-1} = \{(a, c) \mid \exists b \text{ such that } (a, b) \in R \text{ and } (b, c) \in R^{-1}\}.

Step 2: Compute RR1R \circ R^{-1}

To compute RR1R \circ R^{-1}, consider all (a,b)R(a, b) \in R and (b,c)R1(b, c) \in R^{-1}:

  1. From R={(1,2),(1,3),(3,2)}R = \{(1, 2), (1, 3), (3, 2)\}, the possible bb-values are 22 and 33.
  2. From R1={(2,1),(3,1),(2,3)}R^{-1} = \{(2, 1), (3, 1), (2, 3)\}, the bb-values match with aa-values from RR, resulting in (a,c)(a, c) pairs.

Match and compute:

  • For (1,2)R(1, 2) \in R and (2,1)R1(2, 1) \in R^{-1}: (1,1)(1, 1) is in RR1R \circ R^{-1}.
  • For (1,2)R(1, 2) \in R and (2,3)R1(2, 3) \in R^{-1}: (1,3)(1, 3) is in RR1R \circ R^{-1}.
  • For (1,3)R(1, 3) \in R and (3,1)R1(3, 1) \in R^{-1}: (1,1)(1, 1) is in RR1R \circ R^{-1} (already included).
  • For (1,3)R(1, 3) \in R and (3,1)R1(3, 1) \in R^{-1}: (1,1)(1, 1) is repeated.
  • For (3,2)R(3, 2) \in R and (2,1)R1(2, 1) \in R^{-1}: (3,1)(3, 1) is in RR1R \circ R^{-1}.
  • For (3,2)R(3, 2) \in R and (2,3)R1(2, 3) \in R^{-1}: (3,3)(3, 3) is in RR1R \circ R^{-1}.

Thus: RR1={(1,1),(1,3),(3,1),(3,3)}.R \circ R^{-1} = \{(1, 1), (1, 3), (3, 1), (3, 3)\}.


Step 3: Domain and Range

  • The domain of RR1R \circ R^{-1}, Dom(RR1)\text{Dom}(R \circ R^{-1}), is the set of all aa such that (a,c)RR1(a, c) \in R \circ R^{-1}: Dom(RR1)={1,3}.\text{Dom}(R \circ R^{-1}) = \{1, 3\}.

  • The range of RR1R \circ R^{-1}, Ran(RR1)\text{Ran}(R \circ R^{-1}), is the set of all cc such that (a,c)RR1(a, c) \in R \circ R^{-1}: Ran(RR1)={1,3}.\text{Ran}(R \circ R^{-1}) = \{1, 3\}.


Final Answer:

  1. RR1={(1,1),(1,3),(3,1),(3,3)}R \circ R^{-1} = \{(1, 1), (1, 3), (3, 1), (3, 3)\}
  2. Dom(RR1)={1,3}\text{Dom}(R \circ R^{-1}) = \{1, 3\}
  3. Ran(RR1)={1,3}\text{Ran}(R \circ R^{-1}) = \{1, 3\}

Questions:

  1. What is the general formula for RR1R \circ R^{-1} in terms of any set RR?
  2. How do inverse relations affect the domain and range of a relation?
  3. Can RR1R \circ R^{-1} ever produce a relation that includes elements not in A×AA \times A?
  4. How would RRR \circ R differ from RR1R \circ R^{-1} in this context?
  5. Can you identify whether RR1R \circ R^{-1} is reflexive, symmetric, or transitive?

Tip: When composing relations, check for matching elements in both sets to simplify calculations.

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Math Problem Analysis

Mathematical Concepts

Set Theory
Relations and Functions
Inverse Relations
Composition of Relations

Formulas

R^{-1} = {(b, a) | (a, b) ∈ R}
R ◦ R^{-1} = {(a, c) | ∃b such that (a, b) ∈ R and (b, c) ∈ R^{-1}}
Dom(R ◦ R^{-1}) = {a | (a, c) ∈ R ◦ R^{-1}}
Ran(R ◦ R^{-1}) = {c | (a, c) ∈ R ◦ R^{-1}}

Theorems

Properties of Inverse Relations
Composition of Relations Theorem
Domain and Range Definition

Suitable Grade Level

Undergraduate Mathematics or Advanced High School (Grades 11-12)