Calculating values of trig functions

  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. Read this

    or try a web search for "CORDIC."
     
    Last edited: Feb 25, 2005
  4. 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]

    Cosine:

    [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. HallsofIvy

    HallsofIvy 40,229
    Staff Emeritus
    Science Advisor

    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. Really? Strange... I was just told that... oh well.
     
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