Constructibility of Regular Polygons
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Extending Euclidean Constructions with Dynamic Geometry Software
Proceedings of the 20th Asian Technology Conference in Mathematics (Leshan, China, 2015) Extending Euclidean constructions with dynamic geometry software Alasdair McAndrew [email protected] College of Engineering and Science Victoria University PO Box 18821, Melbourne 8001 Australia Abstract In order to solve cubic equations by Euclidean means, the standard ruler and compass construction tools are insufficient, as was demonstrated by Pierre Wantzel in the 19th century. However, the ancient Greek mathematicians also used another construction method, the neusis, which was a straightedge with two marked points. We show in this article how a neusis construction can be implemented using dynamic geometry software, and give some examples of its use. 1 Introduction Standard Euclidean geometry, as codified by Euclid, permits of two constructions: drawing a straight line between two given points, and constructing a circle with center at one given point, and passing through another. It can be shown that the set of points constructible by these methods form the quadratic closure of the rationals: that is, the set of all points obtainable by any finite sequence of arithmetic operations and the taking of square roots. With the rise of Galois theory, and of field theory generally in the 19th century, it is now known that irreducible cubic equations cannot be solved by these Euclidean methods: so that the \doubling of the cube", and the \trisection of the angle" problems would need further constructions. Doubling the cube requires us to be able to solve the equation x3 − 2 = 0 and trisecting the angle, if it were possible, would enable us to trisect 60◦ (which is con- structible), to obtain 20◦. -
Es, and (3) Toprovide -Specific Suggestions for Teaching Such Topics
DOCUMENT RESUME ED 026 236 SE 004 576 Guidelines for Mathematics in the Secondary School South Carolina State Dept. of Education, Columbia. Pub Date 65 Note- I36p. EDRS Price MF-$0.7511C-$6.90 Deseriptors- Advanced Programs, Algebra, Analytic Geometry, Coucse Content, Curriculum,*Curriculum Guides, GeoMetry,Instruction,InstructionalMaterials," *Mathematics, *Number ConCepts,NumberSystems,- *Secondar.. School" Mathematies Identifiers-ISouth Carcilina- This guide containsan outline of topics to be included in individual subject areas in secondary school mathematics andsome specific. suggestions for teachin§ them.. Areas covered inclUde--(1) fundamentals of mathematicsincluded in seventh and eighth grades and general mathematicsin the high school, (2) algebra concepts for COurset one and two, (3) geometry, and (4) advancedmathematics. The guide was written With the following purposes jn mind--(1) to assist local .grOupsto have a basis on which to plan a rykathematics 'course of study,. (2) to give individual teachers an overview of a. particular course Or several cOur:-:es, and (3) toprovide -specific sUggestions for teaching such topics. (RP) Ilia alb 1 fa...4...w. M".7 ,noo d.1.1,64 III.1ai.s3X,i Ala k JS& # Aso sA1.6. It tilatt,41.,,,k a.. -----.-----:--.-:-:-:-:-:-:-:-:-.-. faidel1ae,4 icii MATHEMATICSIN THE SECONDARYSCHOOL Published by STATE DEPARTMENT OF EDUCATION JESSE T. ANDERSON,State Superintendent Columbia, S. C. 1965 Permission to Reprint Permission to reprint A Guide, Mathematics in Florida Second- ary Schools has been granted by the State Department of Edu- cation, Tallahassee, Flmida, Thomas D. Bailey, Superintendent. The South Carolina State Department of Education is in- debted to the Florida State DepartMent of Education and the aahors of A Guide, Mathematics in Florida Secondary Schools. -
Applying the Polygon Angle
POLYGONS 8.1.1 – 8.1.5 After studying triangles and quadrilaterals, students now extend their study to all polygons. A polygon is a closed, two-dimensional figure made of three or more non- intersecting straight line segments connected end-to-end. Using the fact that the sum of the measures of the angles in a triangle is 180°, students learn a method to determine the sum of the measures of the interior angles of any polygon. Next they explore the sum of the measures of the exterior angles of a polygon. Finally they use the information about the angles of polygons along with their Triangle Toolkits to find the areas of regular polygons. See the Math Notes boxes in Lessons 8.1.1, 8.1.5, and 8.3.1. Example 1 4x + 7 3x + 1 x + 1 The figure at right is a hexagon. What is the sum of the measures of the interior angles of a hexagon? Explain how you know. Then write an equation and solve for x. 2x 3x – 5 5x – 4 One way to find the sum of the interior angles of the 9 hexagon is to divide the figure into triangles. There are 11 several different ways to do this, but keep in mind that we 8 are trying to add the interior angles at the vertices. One 6 12 way to divide the hexagon into triangles is to draw in all of 10 the diagonals from a single vertex, as shown at right. 7 Doing this forms four triangles, each with angle measures 5 4 3 1 summing to 180°. -
Squaring the Circle a Case Study in the History of Mathematics the Problem
Squaring the Circle A Case Study in the History of Mathematics The Problem Using only a compass and straightedge, construct for any given circle, a square with the same area as the circle. The general problem of constructing a square with the same area as a given figure is known as the Quadrature of that figure. So, we seek a quadrature of the circle. The Answer It has been known since 1822 that the quadrature of a circle with straightedge and compass is impossible. Notes: First of all we are not saying that a square of equal area does not exist. If the circle has area A, then a square with side √A clearly has the same area. Secondly, we are not saying that a quadrature of a circle is impossible, since it is possible, but not under the restriction of using only a straightedge and compass. Precursors It has been written, in many places, that the quadrature problem appears in one of the earliest extant mathematical sources, the Rhind Papyrus (~ 1650 B.C.). This is not really an accurate statement. If one means by the “quadrature of the circle” simply a quadrature by any means, then one is just asking for the determination of the area of a circle. This problem does appear in the Rhind Papyrus, but I consider it as just a precursor to the construction problem we are examining. The Rhind Papyrus The papyrus was found in Thebes (Luxor) in the ruins of a small building near the Ramesseum.1 It was purchased in 1858 in Egypt by the Scottish Egyptologist A. -
Properties of N-Sided Regular Polygons
PROPERTIES OF N-SIDED REGULAR POLYGONS When students are first exposed to regular polygons in middle school, they learn their properties by looking at individual examples such as the equilateral triangles(n=3), squares(n=4), and hexagons(n=6). A generalization is usually not given, although it would be straight forward to do so with just a min imum of trigonometry and algebra. It also would help students by showing how one obtains generalization in mathematics. We show here how to carry out such a generalization for regular polynomials of side length s. Our starting point is the following schematic of an n sided polygon- We see from the figure that any regular n sided polygon can be constructed by looking at n isosceles triangles whose base angles are θ=(1-2/n)(π/2) since the vertex angle of the triangle is just ψ=2π/n, when expressed in radians. The area of the grey triangle in the above figure is- 2 2 ATr=sh/2=(s/2) tan(θ)=(s/2) tan[(1-2/n)(π/2)] so that the total area of any n sided regular convex polygon will be nATr, , with s again being the side-length. With this generalized form we can construct the following table for some of the better known regular polygons- Name Number of Base Angle, Non-Dimensional 2 sides, n θ=(π/2)(1-2/n) Area, 4nATr/s =tan(θ) Triangle 3 π/6=30º 1/sqrt(3) Square 4 π/4=45º 1 Pentagon 5 3π/10=54º sqrt(15+20φ) Hexagon 6 π/3=60º sqrt(3) Octagon 8 3π/8=67.5º 1+sqrt(2) Decagon 10 2π/5=72º 10sqrt(3+4φ) Dodecagon 12 5π/12=75º 144[2+sqrt(3)] Icosagon 20 9π/20=81º 20[2φ+sqrt(3+4φ)] Here φ=[1+sqrt(5)]/2=1.618033989… is the well known Golden Ratio. -
Interior and Exterior Angles of Polygons 2A
Regents Exam Questions Name: ________________________ G.CO.C.11: Interior and Exterior Angles of Polygons 2a www.jmap.org G.CO.C.11: Interior and Exterior Angles of Polygons 2a 1 Which type of figure is shown in the accompanying 5 In the diagram below of regular pentagon ABCDE, diagram? EB is drawn. 1) hexagon 2) octagon 3) pentagon 4) quadrilateral What is the measure of ∠AEB? 2 What is the measure of each interior angle of a 1) 36º regular hexagon? 2) 54º 1) 60° 3) 72º 2) 120° 4) 108º 3) 135° 4) 270° 6 What is the measure, in degrees, of each exterior angle of a regular hexagon? 3 Determine, in degrees, the measure of each interior 1) 45 angle of a regular octagon. 2) 60 3) 120 4) 135 4 Determine and state the measure, in degrees, of an interior angle of a regular decagon. 7 A stop sign in the shape of a regular octagon is resting on a brick wall, as shown in the accompanying diagram. What is the measure of angle x? 1) 45° 2) 60° 3) 120° 4) 135° 1 Regents Exam Questions Name: ________________________ G.CO.C.11: Interior and Exterior Angles of Polygons 2a www.jmap.org 8 One piece of the birdhouse that Natalie is building 12 The measure of an interior angle of a regular is shaped like a regular pentagon, as shown in the polygon is 120°. How many sides does the polygon accompanying diagram. have? 1) 5 2) 6 3) 3 4) 4 13 Melissa is walking around the outside of a building that is in the shape of a regular polygon. -
The Construction, by Euclid, of the Regular Pentagon
THE CONSTRUCTION, BY EUCLID, OF THE REGULAR PENTAGON Jo˜ao Bosco Pitombeira de CARVALHO Instituto de Matem´atica, Universidade Federal do Rio de Janeiro, Cidade Universit´aria, Ilha do Fund˜ao, Rio de Janeiro, Brazil. e-mail: [email protected] ABSTRACT We present a modern account of Ptolemy’s construction of the regular pentagon, as found in a well-known book on the history of ancient mathematics (Aaboe [1]), and discuss how anachronistic it is from a historical point of view. We then carefully present Euclid’s original construction of the regular pentagon, which shows the power of the method of equivalence of areas. We also propose how to use the ideas of this paper in several contexts. Key-words: Regular pentagon, regular constructible polygons, history of Greek mathe- matics, equivalence of areas in Greek mathematics. 1 Introduction This paper presents Euclid’s construction of the regular pentagon, a highlight of the Elements, comparing it with the widely known construction of Ptolemy, as presented by Aaboe [1]. This gives rise to a discussion on how to view Greek mathematics and shows the care on must have when adopting adapting ancient mathematics to modern styles of presentation, in order to preserve not only content but the very way ancient mathematicians thought and viewed mathematics. 1 The material here presented can be used for several purposes. First of all, in courses for prospective teachers interested in using historical sources in their classrooms. In several places, for example Brazil, the history of mathematics is becoming commonplace in the curricula of courses for prospective teachers, and so one needs materials that will awaken awareness of the need to approach ancient mathematics as much as possible in its own terms, and not in some pasteurized downgraded versions. -
Formulas Involving Polygons - Lesson 7-3
you are here > Class Notes – Chapter 7 – Lesson 7-3 Formulas Involving Polygons - Lesson 7-3 Here’s today’s warmup…don’t forget to “phone home!” B Given: BD bisects ∠PBQ PD ⊥ PB QD ⊥ QB M Prove: BD is ⊥ bis. of PQ P Q D Statements Reasons Honors Geometry Notes Today, we started by learning how polygons are classified by their number of sides...you should already know a lot of these - just make sure to memorize the ones you don't know!! Sides Name 3 Triangle 4 Quadrilateral 5 Pentagon 6 Hexagon 7 Heptagon 8 Octagon 9 Nonagon 10 Decagon 11 Undecagon 12 Dodecagon 13 Tridecagon 14 Tetradecagon 15 Pentadecagon 16 Hexadecagon 17 Heptadecagon 18 Octadecagon 19 Enneadecagon 20 Icosagon n n-gon Baroody Page 2 of 6 Honors Geometry Notes Next, let’s look at the diagonals of polygons with different numbers of sides. By drawing as many diagonals as we could from one diagonal, you should be able to see a pattern...we can make n-2 triangles in a n-sided polygon. Given this information and the fact that the sum of the interior angles of a polygon is 180°, we can come up with a theorem that helps us to figure out the sum of the measures of the interior angles of any n-sided polygon! Baroody Page 3 of 6 Honors Geometry Notes Next, let’s look at exterior angles in a polygon. First, consider the exterior angles of a pentagon as shown below: Note that the sum of the exterior angles is 360°. -
Växjö University
School of Mathematics and System Engineering Reports from MSI - Rapporter från MSI Växjö University Geometrical Constructions Tanveer Sabir Aamir Muneer June MSI Report 09021 2009 Växjö University ISSN 1650-2647 SE-351 95 VÄXJÖ ISRN VXU/MSI/MA/E/--09021/--SE Tanveer Sabir Aamir Muneer Trisecting the Angle, Doubling the Cube, Squaring the Circle and Construction of n-gons Master thesis Mathematics 2009 Växjö University Abstract In this thesis, we are dealing with following four problems (i) Trisecting the angle; (ii) Doubling the cube; (iii) Squaring the circle; (iv) Construction of all regular polygons; With the help of field extensions, a part of the theory of abstract algebra, these problems seems to be impossible by using unmarked ruler and compass. First two problems, trisecting the angle and doubling the cube are solved by using marked ruler and compass, because when we use marked ruler more points are possible to con- struct and with the help of these points more figures are possible to construct. The problems, squaring the circle and Construction of all regular polygons are still im- possible to solve. iii Key-words: iv Acknowledgments We are obliged to our supervisor Per-Anders Svensson for accepting and giving us chance to do our thesis under his kind supervision. We are also thankful to our Programme Man- ager Marcus Nilsson for his work that set up a road map for us. We wish to thank Astrid Hilbert for being in Växjö and teaching us, She is really a cool, calm and knowledgeable, as an educator should. We also want to thank of our head of department and teachers who time to time supported in different subjects. -
ANCIENT PROBLEMS VS. MODERN TECHNOLOGY 1. Geometric Constructions Some Problems, Such As the Search for a Construction That Woul
ANCIENT PROBLEMS VS. MODERN TECHNOLOGY SˇARKA´ GERGELITSOVA´ AND TOMA´ Sˇ HOLAN Abstract. Geometric constructions using a ruler and a compass have been known for more than two thousand years. It has also been known for a long time that some problems cannot be solved using the ruler-and-compass method (squaring the circle, angle trisection); on the other hand, there are other prob- lems that are yet to be solved. Nowadays, the focus of researchers’ interest is different: the search for new geometric constructions has shifted to the field of recreational mathematics. In this article, we present the solutions of several construction problems which were discovered with the help of a computer. The aim of this article is to point out that computer availability and perfor- mance have increased to such an extent that, today, anyone can solve problems that have remained unsolved for centuries. 1. Geometric constructions Some problems, such as the search for a construction that would divide a given angle into three equal parts, the construction of a square having an area equal to the area of the given circle or doubling the cube, troubled mathematicians already hundreds and thousands of years ago. Today, we not only know that these problems have never been solved, but we are even able to prove that such constructions cannot exist at all [8], [10]. On the other hand, there is, for example, the problem of finding the center of a given circle with a compass alone. This is a problem that was admired by Napoleon Bonaparte [11] and one of the problems that we are able to solve today (Mascheroni found the answer long ago [9]). -
Construction of Regular Polygons a Constructible Regular Polygon Is One That Can Be Constructed with Compass and (Unmarked) Straightedge
DynamicsOfPolygons.org Construction of regular polygons A constructible regular polygon is one that can be constructed with compass and (unmarked) straightedge. For example the construction on the right below consists of two circles of equal radii. The center of the second circle at B is chosen to lie anywhere on the first circle, so the triangle ABC is equilateral – and hence equiangular. Compass and straightedge constructions date back to Euclid of Alexandria who was born in about 300 B.C. The Greeks developed methods for constructing the regular triangle, square and pentagon, but these were the only „prime‟ regular polygons that they could construct. They also knew how to double the sides of a given polygon or combine two polygons together – as long as the sides were relatively prime, so a regular pentagon could be drawn together with a regular triangle to get a regular 15-gon. Therefore the polygons they could construct were of the form N = 2m3k5j where m is a nonnegative integer and j and k are either 0 or 1. The constructible regular polygons were 3, 4, 5, 6, 8, 10, 12, 15, 16, 20, 24, 30, 32, 40, 48, ... but the only odd polygons in this list are 3,5 and 15. The triangle, pentagon and 15-gon are the only regular polygons with odd sides which the Greeks could construct. If n = p1p2 …pk where the pi are odd primes then n is constructible iff each pi is constructible, so a regular 21-gon can be constructed iff both the triangle and regular 7-gon can be constructed. -
Trisect Angle
HOW TO TRISECT AN ANGLE (Using P-Geometry) (DRAFT: Liable to change) Aaron Sloman School of Computer Science, University of Birmingham (Philosopher in a Computer Science department) NOTE Added 30 Jan 2020 Remarks on angle-trisection without the neusis construction can be found in Freksa et al. (2019) NOTE Added 1 Mar 2015 The discussion of alternative geometries here contrasts with the discussion of the nature of descriptive metaphysics in "Meta-Descriptive Metaphysics: Extending P.F. Strawson’s ’Descriptive Metaphysics’" http://www.cs.bham.ac.uk/research/projects/cogaff/misc/meta-descriptive-metaphysics.html This document makes connections with the discussion of perception of affordances of various kinds, generalising Gibson’s ideas, in http://www.cs.bham.ac.uk/research/projects/cogaff/talks/#gibson Talk 93: What’s vision for, and how does it work? From Marr (and earlier) to Gibson and Beyond Some of the ideas are related to perception of impossible objects. http://www.cs.bham.ac.uk/research/projects/cogaff/misc/impossible.html JUMP TO CONTENTS Installed: 26 Feb 2015 Last updated: A very nice geogebra applet demonstrates the method described below: http://www.cut-the-knot.org/pythagoras/archi.shtml. Feb 2017: Added note about my 1962 DPhil thesis 25 Apr 2016: Fixed typo: ODB had been mistyped as ODE (Thanks to Michael Fourman) 29 Oct 2015: Added reference to discussion of perception of impossible objects. 4 Oct 2015: Added reference to article by O’Connor and Robertson. 25 Mar 2015: added (low quality) ’movie’ gif showing arrow rotating. 2 Mar 2015 Formatting problem fixed. 1 Mar 2015 Added draft Table of Contents.