Math Problem Statement

The degree sequence of a graph is the sequence of the degrees of the vertices of the graph in nonincreasing simple graph G is 4, 3, 3,2,2. a) Draw such a graph G. b) What is the degree sequence of complement of G? [3 Marks] p Marks] Prove or disprove that the given statement is a tautology using truth table. [5 Marks]

Solution

Let's break down the problem step by step.

Part (a): Draw a graph GG with degree sequence 4,3,3,2,24, 3, 3, 2, 2

Steps to construct the graph:

  1. We have 5 vertices labeled, say v1,v2,v3,v4,v5v_1, v_2, v_3, v_4, v_5.
  2. The degree sequence means that vertex v1v_1 has degree 4, v2v_2 and v3v_3 have degree 3, and v4v_4 and v5v_5 have degree 2.
  3. Since vertex v1v_1 has degree 4, it must be connected to all other vertices.
  4. Now connect v2v_2 and v3v_3 to ensure they have degree 3, but ensure that v4v_4 and v5v_5 maintain degree 2 by carefully adding edges.

Here’s one possible graph:

  • v1v_1 connects to v2,v3,v4,v5v_2, v_3, v_4, v_5 (giving v1v_1 degree 4).
  • v2v_2 connects to v3v_3 and v4v_4 (now v2v_2 has degree 3).
  • v3v_3 connects to v5v_5 (now v3v_3 has degree 3, and both v4v_4 and v5v_5 have degree 2).

Part (b): Degree sequence of the complement of GG

In the complement of a graph, two vertices are adjacent if and only if they were not adjacent in the original graph.

  1. In the original graph, v1v_1 had degree 4, meaning it was connected to 4 vertices. In the complement graph, v1v_1 will be connected to 0 vertices (since it was connected to everyone).
  2. Vertices v2v_2 and v3v_3 had degree 3 in the original graph, so in the complement, each will be connected to 1 vertex.
  3. Vertices v4v_4 and v5v_5 had degree 2 in the original graph, so in the complement, each will be connected to 3 vertices.

Thus, the degree sequence of the complement graph is: 0,1,1,3,30, 1, 1, 3, 3

Part (c): Prove or disprove that the given statement is a tautology using a truth table

A tautology is a statement that is always true regardless of the truth values of the components.

Let the given statement be PP. Without the explicit statement provided, let's assume it's a logical formula involving variables p,qp, q, and so on. I will guide you through the steps to test it using a truth table.

  1. Identify the logical operators (e.g., AND, OR, NOT, implications).
  2. Create a truth table for all possible truth values of the involved variables.
  3. Evaluate the statement for each combination of truth values.
  4. Check if the final column is all TRUE—if it is, the statement is a tautology; otherwise, it is not.

If you provide the exact statement, I can construct the truth table and proceed with the proof.


Would you like further details or assistance on any of these steps?

Relative Questions:

  1. Can you describe how the degree sequence helps construct a graph?
  2. What are the properties of the complement of a graph?
  3. How would the degree sequence of a graph change if a vertex were removed?
  4. Why are truth tables important in proving logical statements?
  5. How does the degree of vertices affect the structure of a graph?

Tip:

When constructing graphs from a degree sequence, ensure that each step of adding edges keeps the overall degree sequence intact for all vertices involved.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Graph Theory
Graph Complements
Logic
Truth Tables

Formulas

Degree Sequence of a Graph
Degree of Complement Graph

Theorems

Complement Graph Theorem
Tautology Definition

Suitable Grade Level

Grades 11-12