Lund University/LTH Bachelor thesis FMAL01 Approximation of π Abstract The inverse tangent function can be used to approximate π. When approximating π the convergence of infinite series or products are of great importance for the accuracy of the digits. This thesis will present historical formulas used to approximate π, especially Leibniz–Gregory and Machin’s. Also, the unique Machin two-term formulas will be presented and discussed to show that Machin’s way of calculate π have had a great impact on calculating this number. Madeleine Jansson
[email protected] Mentor: Frank Wikstr¨om Examinator: Tomas Persson June 13, 2019 Contents 1 Introduction 2 2 History 2 2.1 – 500 Anno Domini . .2 2.2 1500 – 1800 Anno Domini . .5 2.3 1800 – Anno Domini . .6 2.4 Proofs . .7 2.4.1 Vi`ete’sformula . .7 2.4.2 Wallis’s formula . .9 2.4.3 Irrationality of π ............................. 11 3 Mathematical background 13 3.1 Precision and accuracy . 13 3.2 Convergence of series . 14 3.3 Rounding . 15 4 Gregory–Leibniz formula 17 4.1 History . 18 4.2 Proof . 18 4.3 Convergence . 20 4.4 x = √1 ....................................... 21 3 5 Machin’s formula 22 5.1 History . 22 5.2 Proof . 23 5.3 Convergence . 24 6 Machin-like formulas 26 6.1 Machin-like formula . 27 6.2 Two-term formula . 27 6.3 Complex factors . 28 6.3.1 Euler’s formula . 30 6.3.2 Machin’s formula . 30 6.3.3 Hermann’s formula . 30 6.3.4 Hutton’s formula .