How Much String to String a Cardioid?

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Bibliographic Details
Title: How Much String to String a Cardioid?
Authors: David Richeson
Source: The American Mathematical Monthly. 132:807-812
Publication Status: Preprint
Publisher Information: Informa UK Limited, 2025.
Publication Year: 2025
Subject Terms: Mathematics - Number Theory, Mathematics - History and Overview, History and Overview (math.HO), FOS: Mathematics, Number Theory (math.NT), 51M25, 51M04, 11A07, 20K01, 20K27
Description: A residue design is an artistic geometric construction in which we have $n$ equally-spaced points on a circle numbered 0 through $n-1$ and we join with a line segment each point $k$ to $ak$ modulo $n$ for some fixed $a\ge 2.$ The envelopes of these lines are epicycloids, like cardioids. In this note, we prove that the sum of the lengths of these line segments has a surprisingly simple closed form. In particular, if one wants to make one of these designs with string, it is easy to calculate how much string is required.
8 pages, 3 figures
Document Type: Article
Language: English
ISSN: 1930-0972
0002-9890
DOI: 10.1080/00029890.2025.2529768
DOI: 10.48550/arxiv.2311.15101
Access URL: http://arxiv.org/abs/2311.15101
Rights: arXiv Non-Exclusive Distribution
Accession Number: edsair.doi.dedup.....81bbbbf1a0912d7af4b80c12fb3718b5
Database: OpenAIRE
Description
Abstract:A residue design is an artistic geometric construction in which we have $n$ equally-spaced points on a circle numbered 0 through $n-1$ and we join with a line segment each point $k$ to $ak$ modulo $n$ for some fixed $a\ge 2.$ The envelopes of these lines are epicycloids, like cardioids. In this note, we prove that the sum of the lengths of these line segments has a surprisingly simple closed form. In particular, if one wants to make one of these designs with string, it is easy to calculate how much string is required.<br />8 pages, 3 figures
ISSN:19300972
00029890
DOI:10.1080/00029890.2025.2529768