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Mathematics Dictionary
Dr. K. G. Shih

The Story of Pi
Questions


  • Q01 | - Series : arctan(x) = x - x^3/3 + x^5/5 - x^7/7 + ....
  • Q02 | - Series : (pi)^2 = 6*(1 + 1/(2^2) + 1/(3^2) + ......)
  • Q03 | - Series : (pi)^2 = 8*(1 + 1/(3^2) + 1/(5^2) + ......)
  • Q04 | - Archimedes polygon method to find pi
  • Q05 | - Value of pi to 1000 decimal places
  • Q06 | - Story of pi : Pi and computer
  • Q07 | - Machine-like formula
  • Q08 | - Reference

  • Answers


    Q01. Series : arctan(x) = x - x^3/3 + x^5/5 - x^7/7 + ....

    Series of pi
    • Since arctan(1) = pi/4
    • Hence pi/4 = 1 - 1/3 + 1/5 - 1/7 + .....
    • This series is simple but it coverge very slow
    Gregory's series
    • pi/4 = 1 - 1/3 + 1/5 - 1/7 + ....

    Go to Begin

    Q02. Series : (pi)^2 = 6*(1 + 1/(2^2) + 1/(3^2) + 1/(4^2) + .....

    Keywords
    • 1. To prove it, we use series of sin(x)
    • 2. We also need equation of theory
    Proof
    • Sin(x) = x - (x^3)/(3!) + (x^5)/(5!)- (x^7)/(7!) + ....
    • If sin(x) = 0, the roots are r0 = 0, r1 = pi, r2 = 2*pi, r3 = 3*pi, ....
    • Hence r1, r2, r3, ... are roots of 1 - (x^2)/6 + (x^4)/120 - ..... = 0
    • Let x^2 = u,
        Then the equation becomes 1 - u/6 + (u^2)/120 - .... = 0
      • The roots of equation : u1 = (pi)^2, u2 = (2*pi)^2, u3 = (3*pi)^2
    • Equation theory
      • Equation : a*x^n + b*x^(n-1) + ..... + p*x + q = 0
      • Roots are x1, x2, x3, ....
      • Coefficient of x and roots : 1/x1 + 1/x2 + 1/x3 + ..... = p/q
    • Hence coefficient and roots u
      • 1/u1 + 1/u2 + 1/u3 + ..... = -(-1/6)/1
      • 1/(pi^2) + 1/((2*pi)^2) + 1/((3*pi)^2) + 1/((4*pi)^2) + .... = 1/6
      • Multiply (pi)^2 on both sides
      • 1 + 1/(2^2) + 1/(3^2) + ..... = ((pi)^2)/6

    Go to Begin

    Q03. Series : (pi)^2 = 8*(1 + 1/(3^2) + 1/(5^2) + 1/(7^2) + ....

    Keywords
    • 1. To prove it, we use series of cos(x)
    • 2. We also need equation of theory
    Proof
    • cos(x) = 1 - (x^2)/(2!) + (x^4)/(4!)- (x^6)/(6!) + ....
    • If cos(x) = 0, the roots are r1 = pi/2, r2 = 3*pi/2, r3 = 5*pi/2, ....
    • Hence r1, r2, r3, ... are roots of 1 - (x^2)/2 + (x^4)/24 - ..... = 0
    • Let x^2 = u,
        Then the equation becomes 1 - u/2 + (u^2)/24 - .... = 0
      • The roots of equation : u1 = (pi/2)^2, u2 = (3*pi/2)^2, u3 = (5*pi/2)^2
    • Equation theory
      • Equation : a*x^n + b*x^(n-1) + ..... + p*x + q = 0
      • Roots are x1, x2, x3, ....
      • Coefficient of x and roots : 1/x1 + 1/x2 + 1/x3 + ..... = p/q
    • Hence coefficient and roots u
      • 1/u1 + 1/u2 + 1/u3 + ..... = -(-1/2)/1
      • 1/((pi/2)^2) + 1/((3*pi/2)^2) + 1/((5*pi/2)^2) + .... = 1/2
      • Multiply (pi/2)^2 on both sides
      • 1 + 1/(3^2) + 1/(5^2) + ..... = ((pi/2)^2)/2 = ((pi)^2)/8

    Go to Begin

    Q04. Archimedes polygon method to find pi

    Formula based Archimedes polygon method
    • pi = C*sin(A)
    • Where C = (2^n)/2 and A = 360/(2^n)
    • Where 2^n is the number of sides of polygon
    Example 1 : n = 3
    • pi = ((2^3)/2)*sin(45) = 4*Sqr(2)/2 = 2*Sqr(2)
    Example 1 : n = 5 and use half angle formula
    • pi = ((2^5)/2)*sin(360/32)
    • = 16*Sqr((1 - cos(360/16))/2)
    • = (16/Sqr(2))*Sqr(1 - cos(360/16))
    • = (16/Sqr(2))*Sqr(1 - Sqr(1 + cos(360/8))/2))
    • = 8*Sqr(2 - Sqr(2 + Sqr(2))) = 3.121445

    Go to Begin

    Q05. Value of pi to 1000 decimal places

    Pi Value to 1000 decimal place
    • pi = 3.
    • 1415926535 8979323846 2643383279 5028841971
    • 6939937510 5820974944 5923078164 0628620899
    • 8628034825 3421170679 8214808651 3282306647
    • 0938446095 5058223172 5359408128 4811174502
    • 8410270193 8521105559 6446229489 5493038196
    • 4428810975 6659334461 2847564823 3786783165
    • 2712019091 4564856692 3460348610 4543266482
    • 1339360726 0249141273 7245870066 0631558817
    • 4881520920 9628292540 9171536436 7892590360
    • 0113305305 4882044652 1384146951 9415116094
    • 3305727036 5759591953 0921861173 8193261179
    • 3105118548 0744623799 6274956735 1885752724
    • 8912279381 8301194912 9833673362 4406566430
    • 8602139494 6395224737 1907021798 6094370277
    • 0539217176 2931767523 8467481846 7669405132
    • 0005681271 4526356082 7785771342 7577896091
    • 7363717872 1468440901 2249534301 4654958537
    • 1050792279 6892589235 4201995611 2129021960
    • 8640344181 5981362977 4771309960 5187072113
    • 4999999837 2978044951 0597317328 1609631859
    • 5024459455 3469083026 4252230825 3344685035
    • 2619311881 7101000313 7838752886 5875332083
    • 8142061717 7669147303 5982534904 2875546873
    • 1159562863 8823537875 9375195778 1857780532

    Go to Begin

    Q06. Story of pi

  • Pi = 3.141592....
    • (1) To 1000 decimal place : see Computer Math p47
    • (2) Story of Pi (See Computer Math Chapter 6)
    • (3) New record : 106 billion decimal places (Genume 2002) by Janpanese scientists

    Pi and Computers
    • 1949 ENIAC was used to compute Pi to 2037 decimal places.
    • 1961 IBM 7090 computed Pi to 100000 decimal places by Shanks and Wrench.
    • 1966 IBM Stretch supercomputer computed pi to 250000 decimal places.
    • 1983 Pi is computed to 16 million decimal places.
    • 1987 Pi is calculated to 134 million decimal places
      • by Yasumasa Kanada of the University of Tokoyo
      • using Nippon Electronic SX-2 supercomputer
    • 1989 Pi calculated to 1;011;196;691 decimal places
      • by David and Gregory Chudnovsky at the Columbia University; New York
      • The calculation was performed twice on an IBM
      • 3090 mainframe and on a Cray-2 supercomputer; and the
      • results matched.
    • 1991 Brothers David and Gregory Chudnovsky
      • use a formula of their discovery and low budget supercomputer
      • to compute pi to 2.1 billion decimal places

    References
    • Augarten; Stan 1984
      • Bit by bit : an illustrated history of computers.
      • Ticknor and Fields; New york; 324p.
    • Freedman; Allan 1989
      • The computer glossary; 4th edition. AMACOM; Division of
      • American Management Association; 776p.
    • Ralston; Anthony and Reilly; Edwin D. 1993
      • Encyclopedia of computer science. Third edition. Van
      • Nostrand Reinhold; New York; 1558p.
    • Taylor; C. F.; Jr. 1988
      • Master handbook of microcomputer languages; 2nd
      • edition; Tak Book; Inc.; Blue Ridge Summit; PA; U.S.A. 499p.
    • Microsoft Press; 1991
      • Computer dictionary : The comprehensive standard for
      • business; school; library and home. Microsoft Press. 392p.

    Go to Begin

    Q07. Machine-like formula

    Machine-like formula
    • 1. Euler's formula : pi/4 = arctan(1/2) + arctan(1/3)
    • 2. Hermann's formula : pi/4 = 2*arctan(1/2) - arctan(1/7)
    • 3. Hutton's formula : pi/4 = 2*arct(1/3) + arctan(1/7)

    Go to Begin

    Q08. Reference

    Book
    • Story of pi
    • Chapter 6, p47 - p54
    • Computer Mathematics by Dr. Keh-Gong Shih
    • Published by National Institute For Compilation and Translation
    • Taipei, Taiwan. 1993. pp 262
    Story of e, i, pi
    • Euler : Introduced e, i, and pi to mathematics
    • Story of e>
    • 1. Select number theory
    • 2. Select constant
    • 3. Select e
    • Story of PI
    • 1. Select number theory
    • 2. Select constant
    • 3. Select pi

    Go to Begin

    Q08. Answer

    Go to Begin

    Q09. Answer

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    Q10. Answer

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    Copyright © Dr. K. G. Shih, Nova Scotia, Canada.

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