Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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?

    THanks!
     
  2. jcsd
  3. Feb 24, 2008 #2

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

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

    Gib Z

    User Avatar
    Homework Helper

    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

    Hurkyl

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

  7. Feb 24, 2008 #6

    Defennder

    User Avatar
    Homework Helper

    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?

    Like:

    http://en.wikipedia.org/wiki/Leibniz_formula_for_pi

    Or this:
    http://www.geom.uiuc.edu/~huberty/math5337/groupe/expresspi.html
    http://en.wikipedia.org/wiki/Computing_π
     
    Last edited: Feb 24, 2008
  8. Feb 25, 2008 #7

    symbolipoint

    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    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
  11. Feb 26, 2008 #10

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    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:
    http://education.ti.com/educationportal/sites/US/productDetail/us_baii_plus.html?bid=6
     
  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)

    Consequence:

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

    So: Pi=sin(dalpha)*180/dalpha
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: How to get PI without the PI key?
  1. How is pi derived? (Replies: 14)

  2. How is pi generated? (Replies: 6)

Loading...