Golden Ratio, Silver Ratio and other Metallic Means ; Geometric Substantiation of all Metallic Ratios

This paper introduces the concept of special right angled triangles those epitomize the different Metallic Ratios. These right triangles not only have the precise Metallic Means embedded in all their geometric features, but they also provide the most accurate geometric substantiation of all Metallic Means. These special right triangles manifest the corresponding Metallic Ratios more holistically than the regular pentagon, octagon or tridecagon, etc

Fórmulas de “Trigonometría Áurea” para las funciones Seno y Coseno

En este artículo, se define una nueva constante matemática (que llamamos b), cuyas propiedades junto con las del número áureo , permiten obtener expresiones algebraicas muy sencillas para las funciones trigonométricas seno y coseno evaluadas en diferentes ángulos. Se obtuvo una sencilla expresión para el área de un pentágono regular inscrito en un círculo de radio 1. Los cálculos de las fórmulas que nos dan el valor de las funciones trigonométricas, expresadas en función de las constantes f y b, se resumen en dos cuadros al final del artículo. Los cuadros se crearon siguiendo un procedimiento análogo al utilizado por el astrónomo Ptolomeo, para hallar los valores numéricos de su famosa tabla de cuerdas, que fue documentado en el primer libro de su gran obra "El Almagesto". Abstract In this paper, a new mathematical constant is defined (we called it b), whose properties along with the golden number’s properties, allow us to obtain very simple algebraic expressions for the trigonometric functions sine and cosine evaluated in different angles. We obtained a simple expression for the area of a regular pentagon inscribed within a circle with radio 1. The calculations of the formulas giving us the value of the trigonometric functions, expressed as a function of the constants f and b, are summarized in two tables at the end of this paper. The tables were created following an analogous procedure as the one used by the astronomer Ptolemy, to find the numerical values of his famous table of chords, documented in the first book of his great work "The Almagest".

Calibrations for minimal networks in a covering space setting

In this paper, we define a notion of calibration for an approach to the classical Steiner problem in a covering space setting and we give some explicit examples. Moreover, we introduce the notion of calibration in families: the idea is to divide the set of competitors in a suitable way, defining an appropriate (and weaker) notion of calibration. Then, calibrating the candidate minimizers in each family and comparing their perimeter, it is possible to find the minimizers of the minimization problem. Thanks to this procedure we prove the minimality of the Steiner configurations spanning the vertices of a regular hexagon and of a regular pentagon.

Generalized Second Moment of Areas of Regular Polygons for Ludwick Type Material and its Application to Cantilever Column Buckling

This study deals with the generalized second moment of area (GSMA) of regular polygon cross-sections for the Ludwick type material and its application to cantilever column buckling. In the literature, the GSMA for the Ludwick type material has only been considered for rectangular, elliptical and superellipsoidal cross-sections. This study calculates the GSMAs of regular polygon cross-sections other than those mentioned above. The GSMAs calculated by varying the mechanical constant of the Ludwick type material for the equilateral triangle, square, regular pentagon, regular hexagon and circular cross-sections are reported in tables and figures. The GSMAs obtained from this study are applied to cantilever column buckling, with results shown in tables and figures.

Paper-folding and cutting activities to demonstrate five-fold symmetry

We can obtain a two-fold symmetric figure by folding a square sheet of paper in the middle and then cutting along some curves drawn on the paper. By making two perpendicular folds through the centre of the paper and then cutting, we can obtain a four-fold symmetric figure. We can also get an eight-fold symmetric figure by making a fold bisecting an angle made by the two perpendicular folds before cutting. But it is not possible to obtain a three-fold, five-fold or six-fold symmetric figure in this way; we need to make more folds before cutting. Making a three-fold (respectively five-fold and six-fold) figure involves the division of the angle at the centre (360°) of a square sheet of a paper into six (respectively ten and twelve) equal parts. In other words, we need to construct the angles 60°, 36° and 30°. But these angles cannot be obtained by repeated bisections of 180° by simple folding as in the making of two-fold, four-fold and eight-fold figures. In [1], we see that each of the constructions of 60° and 30° applies the fact that sin 30° = ½ and takes only a few simple folding steps. The construction of 36° is more tedious (see, for example, [2] and [3]) as sin 36° is not a simple fraction but an irrational number. In this Article, we show how to make, by paper-folding and cutting a regular pentagon, a five-pointed star and create any five-fold figure as we want. The construction obtained by dividing the angle at the centre of a square paper into ten equal parts is called apentagon base. We gained much insight from [2] and [3] when developing the method for making the pentagon base to be presented below.

Golden Ratio and Fibonacci Sequence in Pentagonal Constructions of Medieval Architecture

The construction of the regular pentagon has always meant a difficult geometrical exercise for architects during the Middle Ages. As the correct drafting was forgotten after the Antiquity, several methods for its approximation had been invented in medieval times. As Golden Ratio appears between several parts of the regular pentagon, the role of the Fibonacci sequence in these approximate constructions is to be examined. The pentagonal drawing in the sketchbook of Villard de Honnecourt calls our attention to a possible way how medieval architects could have applied simple numerical ratios for getting angles they needed. The approximation of 72°, for instance, is likely to have been crucial for this pentagonal construction, as well as the approximation of Golden Ratio that could have been achieved by neighbouring pairs from Fibonacci’s sequence.