Math Problem Statement

Total number of reflexive relations on a set with three elements is 2", then nis

Solution

The problem involves determining the value of nn for which the total number of reflexive relations on a set with nn elements is equal to 2.

Reflexive Relation:

A relation RR on a set AA is reflexive if every element of AA is related to itself. In a set with nn elements, say A={a1,a2,,an}A = \{a_1, a_2, \dots, a_n\}, the relation RR will be reflexive if (ai,ai)R(a_i, a_i) \in R for all ii from 1 to nn.

Number of Reflexive Relations:

The total number of reflexive relations on a set with nn elements is calculated as follows:

  1. Total pairs in the Cartesian product A×AA \times A: n2n^2.
  2. Pairs that must be included to ensure reflexivity: nn pairs (ai,ai)(a_i, a_i), where i=1,2,,ni = 1, 2, \dots, n.
  3. Remaining pairs (ai,aj)(a_i, a_j) where iji \neq j: There are n2nn^2 - n such pairs, and each of these pairs can either be included in or excluded from the relation.

Hence, the total number of reflexive relations on a set with nn elements is: 2n2n2^{n^2 - n}

Given:

2n2n=22^{n^2 - n} = 2

This equation simplifies to: n2n=1n^2 - n = 1

This is a quadratic equation: n2n1=0n^2 - n - 1 = 0

Solving the quadratic equation:

We use the quadratic formula: n=b±b24ac2an = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} Here, a=1a = 1, b=1b = -1, and c=1c = -1. Plugging in the values: n=(1)±(1)24(1)(1)2(1)=1±1+42=1±52n = \frac{-(-1) \pm \sqrt{(-1)^2 - 4(1)(-1)}}{2(1)} = \frac{1 \pm \sqrt{1 + 4}}{2} = \frac{1 \pm \sqrt{5}}{2}

Since nn must be a positive integer, we need n2n=1n^2 - n = 1. Testing small integer values of nn:

For n=1n = 1: n2n=121=0(does not satisfy the equation)n^2 - n = 1^2 - 1 = 0 \quad \text{(does not satisfy the equation)}

For n=2n = 2: n2n=222=42=2(does not satisfy the equation)n^2 - n = 2^2 - 2 = 4 - 2 = 2 \quad \text{(does not satisfy the equation)}

Since the equation has no positive integer solution that exactly satisfies n2n=1n^2 - n = 1, the quadratic equation provides irrational roots, meaning no such nn exists as a positive integer solution.

Therefore, there seems to be no integer nn for which the total number of reflexive relations equals 2 under the provided formulation. The premise given may involve an error.

Would you like to ask about a different problem or explore this further?


Related Questions:

  1. What are reflexive relations, and how do they differ from symmetric and transitive relations?
  2. How do you calculate the total number of relations on a set?
  3. What are the steps to solve a quadratic equation using the quadratic formula?
  4. How do reflexive relations change with the number of elements in a set?
  5. Can you explain other types of relations on sets, such as antisymmetric or equivalence relations?
  6. How would the number of reflexive relations change for a set with four elements?
  7. What is the significance of the number of reflexive relations in a set theory?
  8. How can quadratic equations be solved by factoring instead of using the quadratic formula?

Tip: When solving quadratic equations, always consider both roots but ensure the context fits the problem's requirements for the solution.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Set Theory
Reflexive Relations
Quadratic Equations

Formulas

Quadratic formula

Theorems

-

Suitable Grade Level

High School