Triangle areas in line arrangements

Damásdi, Gábor and Martínez-Sandoval, Leonardo and Nagy, Dániel and Nagy, Zoltán Lóránt (2020) Triangle areas in line arrangements. DISCRETE MATHEMATICS, 343 (12). ISSN 0012-365X

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Abstract

A widely investigated subject in combinatorial geometry, originated from Erd}os, is the following. Given a point set P of cardinality n in the plane, how can we describe the distribution of the determined distances? This has been generalized in many directions. In this paper we propose the following variants. What is the maximum number of triangles of unit area, maximum area or minimum area, that can be determined by an arrangement of n lines in the plane? We prove that the order of magnitude for the maximum occurrence of unit areas lies between Omega(n^2) and O(n^9/4+epsilon), for every epsilon > 0. This result is strongly connected to additive combinatorial results and Szemeredi-Trotter type incidence theorems. Next we show an almost tight bound for the maximum number of minimum area triangles. Finally, we present lower and upper bounds for the maximum area and distinct area problems by combining algebraic, geometric and combinatorial techniques.

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