Interior Diagonal of Polygons: Proving Existence

  • Thread starter Thread starter ehrenfest
  • Start date Start date
  • Tags Tags
    Interior
Click For Summary
SUMMARY

Every polygon with more than three sides possesses at least one interior diagonal. This conclusion is derived from the properties of convex polygons, where the existence of diagonals is evident. For non-convex polygons, the presence of an interior angle greater than 180 degrees at a vertex ensures that a ray emanating from that vertex will intersect another vertex, thereby confirming the existence of an interior diagonal. The discussion emphasizes the necessity of demonstrating that rays from a vertex can indeed intersect non-adjacent edges, solidifying the proof.

PREREQUISITES
  • Understanding of polygon properties, specifically convex and non-convex polygons
  • Familiarity with geometric concepts such as interior angles and rays
  • Knowledge of basic proof techniques in geometry
  • Ability to visualize geometric shapes and their properties
NEXT STEPS
  • Research the properties of convex and non-convex polygons in depth
  • Study geometric proof techniques, focusing on ray intersection and angle properties
  • Explore examples of polygons with varying numbers of sides to identify interior diagonals
  • Learn about the implications of interior angles greater than 180 degrees in polygon geometry
USEFUL FOR

Students studying geometry, mathematics educators, and anyone interested in understanding the properties of polygons and their diagonals.

ehrenfest
Messages
2,001
Reaction score
1

Homework Statement


I want to show that every polygon with more than 3 sides has an interior diagonal.

Homework Equations


The Attempt at a Solution



If the polygon is convex, this is obvious. If not, there is an interior angle at some vertex, say V, that is greater than 180 degrees. Then I think a ray emanating from V and sweeping the interior of the polygon must strike another vertex. I cannot find a counterexample to that, but I am not sure how to prove that. It seems like the polygon would be infinite if that is not true, but how can I explain that?
 
Physics news on Phys.org
If the rays from the vertex don't hit another vertex then the first side that they hit must be the same side no matter what the angle. So if you are viewing a segment from a point can it sweep an angle of over 180 degrees?
 
You might be able to start by showing that there is an internal line from your vertex to a non-adjacent edge of the polygon.
 

Similar threads

Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
17
Views
3K