Calculating values of trig functions

by Felix83
Tags: functions, trig, values
Felix83 is offline
Feb25-05, 10:06 AM
P: 75
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?
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CrankFan is offline
Feb25-05, 10:15 AM
P: 135
Read this

or try a web search for "CORDIC."
Moo Of Doom
Moo Of Doom is offline
Feb26-05, 03:08 AM
P: 367
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.

HallsofIvy is offline
Feb26-05, 09:53 AM
Sci Advisor
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P: 38,900

Calculating values of trig functions

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.
Moo Of Doom
Moo Of Doom is offline
Feb26-05, 12:48 PM
P: 367
Really? Strange... I was just told that... oh well.

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