Counting intersections of lines in a triangle

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SUMMARY

The discussion centers on the mathematical problem of counting the intersections of lines drawn from vertices of a triangle to points dividing the opposite sides into equal segments. Specifically, it explores the equation abc = (n-a)(n-b)(n-c) to find integer solutions for odd and even values of n. The conversation reveals that while solutions for even n are straightforward, odd n presents complexities, with participants sharing various approaches and conjectures regarding the number of regions formed and the nature of intersections.

PREREQUISITES
  • Understanding of basic geometry, particularly triangles and their properties.
  • Familiarity with integer solutions in algebraic equations.
  • Knowledge of combinatorial geometry, specifically regarding regions formed by intersecting lines.
  • Basic concepts of modular arithmetic as applied to equations.
NEXT STEPS
  • Research the properties of integer solutions to polynomial equations, focusing on abc = (n-a)(n-b)(n-c).
  • Explore combinatorial geometry techniques for counting regions formed by intersecting lines.
  • Study modular arithmetic and its applications in solving algebraic equations.
  • Investigate constrained optimization problems in geometric contexts.
USEFUL FOR

Mathematicians, geometry enthusiasts, and students studying algebraic geometry or combinatorial geometry who are interested in the properties of triangles and line intersections.

  • #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
 

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