Proof of Degree 5/6 for Graph Theory: Pigeonhole Principle

Click For Summary
SUMMARY

The discussion centers on proving that in a graph with nine vertices, where each vertex has a degree of either 5 or 6, there must be at least five vertices with a degree of 6 or at least six vertices with a degree of 5. Utilizing the Pigeonhole Principle, participants explore the implications of having fewer than five vertices of degree 6, leading to a logical conclusion about the distribution of vertex degrees. The conclusion is that if fewer than five vertices have degree 6, then the remaining vertices must all have degree 5, which contradicts the total vertex count.

PREREQUISITES
  • Understanding of graph theory concepts, specifically vertex degree.
  • Familiarity with the Pigeonhole Principle in combinatorial mathematics.
  • Basic knowledge of logical reasoning and proof techniques.
  • Ability to analyze vertex distributions in finite graphs.
NEXT STEPS
  • Study the Pigeonhole Principle in detail to understand its applications in combinatorial proofs.
  • Explore advanced graph theory topics, including vertex connectivity and degree sequences.
  • Learn about other proof techniques in mathematics, such as contradiction and induction.
  • Investigate real-world applications of graph theory in computer science and network analysis.
USEFUL FOR

Students of mathematics, particularly those studying graph theory, educators teaching combinatorial proofs, and researchers interested in mathematical logic and its applications.

smiles988
Messages
6
Reaction score
0
1. Suppose a graph has nine vertices each of degree 5 or 6. Prove that at least five vertices have degree 6 or at least six vertices have degree 5.



Homework Equations





3. I'm pretty sure that I need to use the Pigeonhole Principle to solve, but don't know where to go from there.
 
Physics news on Phys.org
Suppose the graph has fewer than 5 vertices of degree 6. How many vertices does that leave? What degree do those vertices have?
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
Replies
4
Views
2K
  • · Replies 22 ·
Replies
22
Views
4K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 12 ·
Replies
12
Views
4K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 34 ·
2
Replies
34
Views
6K
  • · Replies 3 ·
Replies
3
Views
1K