Finding sin and cos without using calculator

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Finding sine and cosine without a calculator can be achieved using Taylor series, which provide approximations for these functions near zero. The series for sine and cosine are given by sin(x) = x - x^3/3! + x^5/5! - ... and cos(x) = 1 - x^2/2! + x^4/4! - ..., respectively. While this method allows for increasing accuracy by adding more terms, it can become tedious without a calculator for evaluating the series. Additionally, calculators typically do not use Taylor series for trigonometric functions due to slow convergence, opting for more efficient algorithms instead. Alternative methods, such as using right triangles or the CORDIC algorithm, can also be employed to find sine and cosine values.
Emmanuel_Euler
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Hi everyone.
i think this is my last thread on PF:frown:!
because i am too busy,anyway,
4 months ago i posted a thread named it finding cube roots without using calculator and now i want to know if there is a way or method to find sin and cos without using calculator.
And thanks to all who helped me in all of my questions.
 
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You can get as close as you want by using a Taylor series.

\sin(x) = x - \frac{x^3}{3!} + \frac{x^5}{5!} - \ ...

\cos(x) = 1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \ ...

This works well for x near 0. Just cut it off at however many terms you want depending on how accurate you want it. You could use a more general form for the functions starting at any x = a, but given their periodicity, it seems the simplified would work fine. The only issue then is adding up some fractions.
 
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axmls said:
You can get as close as you want by using a Taylor series.

\sin(x) = x - \frac{x^3}{3!} + \frac{x^5}{5!} - \ ...

\cos(x) = 1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \ ...

This works well for x near 0. Just cut it off at however many terms you want depending on how accurate you want it. You could use a more general form for the functions starting at any x = a, but given their periodicity, it seems the simplified would work fine. The only issue then is adding up some fractions.
Maybe you can use a Taylor series to evaluate a trig function without pressing the sin x or cos x keys on a calculator, but I think actually evaluating the Taylor series without using the other calculator functions will get a bit tedious, especially as you add more terms to the evaluation.
 
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SteamKing said:
Maybe you can use a Taylor series to evaluate a trig function without pressing the sin x or cos x keys on a calculator, but I think actually evaluating the Taylor series without using the other calculator functions will get a bit tedious, especially as you add more terms to the evaluation.
should i have a Calculator function to evaluate taylor series??
 
Emmanuel_Euler said:
should i have a Calculator function to evaluate taylor series??
No. And your calculator wouldn't use Taylor series to calculate the value of sin x or cos x, either. The Taylor series is slow to converge, and calculators with built-in trig functions use different methods to calculate their values.

https://en.wikipedia.org/wiki/CORDIC
 
What came to my mind when you said that was draw out a triangle with the angle you want to measure and then divide the hypothenuse by the adjacent for cos and the opposite for sin??
 
This is similar to what SteamKing wrote. The ##\cos z## and ##\sin z## functions respectively are just real and imaginary parts of ##e^{iz}##. We can calculate the sine and cosine functions (in radians) by calculating the real and imaginary parts of the series,

\sum_{n=0}^{\infty} {\frac{(-1)^{\frac{n}{2}} z^n}{n!}}
 
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