5.Q.1. NUMBER OF INTERSECTIONS DETERMINED BY N LINES
Chrystal. Text Book of Algebra. 2nd ed., vol. 2, 1889, p. 34, ex. 7. See above.
Loyd Jr. SLAHP. 1928. When drummers meet, pp. 74 & 115. Six straight railroads can meet in 15 points.
Paul Erdös, proposer; Norbert Kaufman & R. H. Koch and Arthur Rosenthal, solvers. Problem E750. AMM 53 (1946) 591 & 54 (1947) 344. The first solution is given in Trigg, op. cit. in 5.Q, Quickie 191: Intersections of diagonals, pp. 53 & 166 167. In a convex n gon, how many intersections of diagonals are there? This counts a triple intersection as three ordinary (i.e. double) intersections or assumes no three diagonals are concurrent. Editorial notes add some extra results and cite Chrystal.
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