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Plane Geometry - Bruce E. Shapiro

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242 SECTION 44. ESTIMATING πso thatand so forth.H 2 = √ 2»H 3 = 2 − √ 2√ »H 4 = 2 − 2 + √ 2… √ »H 5 = 2 − 2 + 2 + √ 2… √ »H 6 = 2 − 2 + 2 + 2 + √ 2One could, for example, calculate the first i values of π i with the followingcode in Mathematica:f[x_]:= Sqrt[2*(1-Sqrt[1-(x/2)^2])];pi[i_] := NestList[f, Sqrt[2], i]*Table[2^n, {n, 1, i + 1}];To print the first 25 estimates to 20 significant figures, we enterN[pi[25],20]The resulting guesses would be{2.8284271247461900976, 3.0614674589207181738,3.1214451522580522856, 3.1365484905459392638,3.1403311569547529123, 3.1412772509327728681,3.1415138011443010763, 3.1415729403670913841,3.1415877252771597006, 3.1415914215111999740,3.1415923455701177423, 3.1415925765848726657,3.1415926343385629891, 3.1415926487769856695,3.1415926523865913458, 3.1415926532889927653,3.1415926535145931202, 3.1415926535709932089,3.1415926535850932311, 3.1415926535886182366,3.1415926535894994880, 3.1415926535897198008,3.1415926535897748791, 3.1415926535897886486,3.1415926535897920910, 3.1415926535897929516}The correct value of π to 20 figures is 3.1415926535897932385.Method of ArchimedesArchimedes estimated the value of π by assuming that the perimeter I n ofany inscribed regular n-sided polygon was less than the circumference ofa circle, and the perimeter C n of any regular-sided circumscribed polygonwas greater than the circumference of the same circle:I n < C < C n« CC BY-NC-ND 3.0. Revised: 18 Nov 2012

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