An infinite product of nested radicals for log x from the Archimedean algorithm. Issue 548 (14th June 2016)

• Record Type: Journal Article
• Authors: Osler, Thomas J.; Jacob, Walter; Nishimura, Ryo
• Is Part Of: Mathematical gazette. Volume 100:Issue 548(2016)
• Page Start: 274
• Page End: 278
• Publication Date: 2016-06-14
• Subjects: Mathematics -- Periodicals; Mathématique; Mathematik; Mathematics; Periodicals; Ressource Internet (Descripteur de forme); Périodique électronique (Descripteur de forme); Zeitschrift; Online-Publikation; 510
• DOI: 10.1017/mag.2016.64
• Languages: English
• ISSNs: 0025-5572

Abstract

Abstract : The so-called Archimedean iterative algorithm for calculating π uses a method involving the two equations (1) and (2) (Note that (1) is the harmonic mean.) Imagine two regular polygons each with the same number of sides, circumscribed and inscribed to a circle of diameter one. The larger one has perimeter a 0, the smaller has perimeter b 0 . (Archimedes used hexagons with and b 0 = 3, but regular polygons of any number of sides can begin the iterations.) Since the perimeter of the circle is π we have b 0 < π < a 0 . Now consider regular polygons with twice the number of sides that circumscribe and inscribe the circle and call their perimeters a 1 and b 1 respectively. These can be calculated, from (2) and (3). (See [1] for a derivation or many explanations on the web.) Continuing in this way we generate the perimeters of inscribed and circumscribed regular polygons, and in each case the number of sides is twice the sides of the previous polygon.