Counting intersections of lines in a triangle

Click For Summary

Discussion Overview

The discussion revolves around the problem of counting intersections of lines drawn from the vertices of a triangle to points dividing the opposite sides into equal segments. Participants explore the implications of these intersections on the formation of regions within the triangle, as well as the conditions under which certain integer solutions exist for the equation abc = (n-a)(n-b)(n-c). The scope includes theoretical exploration and mathematical reasoning related to geometry and combinatorial counting.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant proposes dividing each side of a triangle into n equal lengths and connecting the ends to the opposite vertex, forming overlapping triangles of equal area.
  • Another participant discusses the number of regions formed by lines drawn from the vertices and suggests a formula for calculating these regions based on the number of lines from each vertex.
  • There is a claim that if there are no points where three lines intersect, the total number of regions can be calculated by a specific formula involving n.
  • Some participants express uncertainty about the implications of odd and even values of n on the existence of integer solutions to the equation abc = (n-a)(n-b)(n-c).
  • One participant provides examples of odd solutions for specific values of n and discusses the scaling of these solutions.
  • Another participant introduces the idea of using a matrix equation to approach the problem as a constrained optimization issue.
  • There is a discussion about the relationship between the number of angles formed and the points of intersection, with a formula proposed for counting corners based on the number of lines drawn.
  • Some participants question how certain modular arithmetic considerations may affect the existence of solutions.

Areas of Agreement / Disagreement

Participants express differing views on the existence of solutions for odd values of n, with some claiming there are solutions while others remain skeptical. The discussion does not reach a consensus on the implications of these findings or the correctness of the proposed formulas.

Contextual Notes

Participants note that certain assumptions about the parameters of the lines and the nature of intersections may limit the applicability of their findings. There are unresolved mathematical steps related to the conditions under which integer solutions exist.

Who May Find This Useful

This discussion may be of interest to those studying geometry, combinatorial mathematics, or anyone exploring the properties of intersections in geometric figures.

  • #31
It generates a large number of solutions, but not all:
n= 35, a= 5 , b= 21 c= 28
As three numbers need a common divisor, we have m=7 as only option (m=1 doesn't fit with the generating equations). This leads to k=5 and c=1:
(7*5 ; 3*7 , 4*7 , 1*5)
We also need 7=1+2*3 (correct) and 1=(5-4)(5-3) (wrong).

k=a+b, k=a+a and k=b+b lead to the trivial solutions.

Code:
15	5	5	12
15	10	10	3
20	5	5	18
20	15	15	2
35	7	14	30
42	7	28	30
55	11	33	40
63	9	27	56
63	21	28	45
65	26	26	45
65	39	39	20
66	11	22	60
72	16	24	63
77	11	44	63
78	13	13	75
85	17	17	80
90	27	36	70
99	11	44	90
112	16	32	105
136	51	51	100
152	19	57	140
175	75	75	112
203	58	58	175
259	37	37	252
290	29	116	270
310	62	93	280
 

Similar threads

  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 31 ·
2
Replies
31
Views
4K
  • · Replies 2 ·
Replies
2
Views
5K
  • · Replies 7 ·
Replies
7
Views
5K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 16 ·
Replies
16
Views
3K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K