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Calculating values of trig functions

  1. Feb 25, 2005 #1
    How does a calculator approximate a trig function. For example, you punch in sin(37deg) and the calculator will give you 0.6018150232. how does it figure this out?
  2. jcsd
  3. Feb 25, 2005 #2
    http://math.exeter.edu/rparris/peanut/cordic.pdf [Broken]

    or try a web search for "CORDIC."
    Last edited by a moderator: May 1, 2017
  4. Feb 26, 2005 #3
    Calculators use partial sums of power series to approximate sine and cosine.

    The power series for sine is:

    [tex]sin(x) = x - \frac{1}{3!} * x^{3} + \frac{1}{5!} * x^{5} - \frac{1}{7!} * x^{7} + ...[/tex]


    [tex]cos(x) = 1 - \frac{1}{2!} * x^{2} + \frac{1}{4!} * x^{4} - \frac{1}{6!} * x^{6} + ...[/tex]

    I'm not sure how many terms they usually use, but that doesn't really matter. The more terms, the more accurate.
  5. Feb 26, 2005 #4


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    Moo Of Doom: I thought for a long time that calculators used power series but I've been told that is not true. Check out CranFan's suggestion about the CORDIC algorithm.
  6. Feb 26, 2005 #5
    Really? Strange... I was just told that... oh well.
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