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How to get PI without the PI key?

  1. Feb 24, 2008 #1
    Hi, I have a BA II plus Prof. and there's no "pi" key, I tried using the trig functions to get the value but it always give me a something in degrees.

    I want to avoid using 22/7 as it's not close enough.
    Is there any way to get the number instead of memorizing it?

  2. jcsd
  3. Feb 24, 2008 #2


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    How about 31415/10000?
  4. Feb 24, 2008 #3

    Gib Z

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    Well, memorizing it to 5 or so digits isnt that hard (I know 15 just in case =] ) and in fact it may be easier to remember than any other method of getting the number on your calculator. I could tell you [tex]\pi \approx \frac{ \log_e ( 640320^3 + 744)}{\sqrt{163}}[/tex], which is accurate to around 70 digits, but thats much harder to memorize, not to mention if the button doesn't have pi, it probably wont have the other functions. Either remember, 3.1415926535 (truncate it earlier if you want) or, even better, 355/113 is good to 7 or so digits.
  5. Feb 24, 2008 #4


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    What's a BA II plus Prof.? I'm going to assume a scientific calculator... most calculators allow you to switch the trig mode between degrees, radians, and gradians.
  6. Feb 24, 2008 #5


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    Here is a link to the TI webpage where you can download a manual:
    http://education.ti.com/educationportal/downloadcenter/SoftwareDetail.do?website=US&tabId=2&appId=6114 [Broken]
    Last edited by a moderator: May 3, 2017
  7. Feb 24, 2008 #6


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    Guys, I think he's looking for a way to write out PI itself without approximating it by whole number division or some other mathematical trick. Meaning to say that he wants to be able to write out PI with some mathematical expression as an number with an infinite decimal places accurately to any precision he wishes. (sorry if I sound a little incoherent, I'm down with fever at present)

    Why not try PI as the sum to infinity of some series?



    Or this:
    Last edited: Feb 24, 2008
  8. Feb 25, 2008 #7


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    Do you mean through a simple calculation to obtain a good or comfortable approximation? Try either memorizing the first six digits, or use a mnemonic method. Try an internet search and you can find something that goes like, "Hey, I need a drink..."; I forgot how the rest of it goes, but count the letters in each word, use the comma as a decimal point, and you find 3.1415...

    Then there is the simple calculation, 1 1 3 3 5 5 arrangement which uses the ratio 355/113
  9. Feb 25, 2008 #8
    What about 2 * Arcsin (1)?
  10. Feb 25, 2008 #9
    This might help:

    http://www.isi.edu/~johnh/ABOUT/FEATURES/RATIONAL_PI/index.html" [Broken]

    Those are rational approximations of Pi up to a tolerance of 2.6621325721620792e-07.
    Last edited by a moderator: May 3, 2017
  11. Feb 26, 2008 #10


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    I don't, I think he is just looking for a way to use "[itex]\pi[/itex]" on his calculator!
    Unfortunately, he hasn't gotten back to us so we can't be sure what he wants.

    The BA II calculator is itself a "financial" calculator and is, apparently, "object oriented" since the manual talks about "objects" that may or may not have "constructors" and have values of functions accessed by a ".". In particular, Chocok, "MATH.E" gives you the value of "e".
    You can find it in your manual, I think on pages 95- 100. If you don't still have the manual, you can find a PDF copy at the website I posted before but here it is again:
  12. Feb 26, 2008 #11
    This works if trig. functions are defined in radians, not in degrees. In the later case I would use the formula:

    sin(dfi)=dfi (radians)


    sin(dalpha)=dalpha*2*Pi/360 (degrees)

    So: Pi=sin(dalpha)*180/dalpha
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