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HP Forum Archive 21

 Easter Sunday Basic Trigs (HP-12C)Message #1 Posted by Gerson W. Barbosa on 31 Mar 2013, 12:59 a.m. ``` HP-12C 01- 3 21- 1/x 02- / 22- + 03- ENTER 23- 2 04- ENTER 24- / 05- 4 25- - 06- y^x 26- ENTER 07- 12/ 27- ENTER 08- ENTER 28- * 09- ENTER 29- 4 10- * 30- * 11- 1 31- 3 12- 4 32- - 13- 0 33- * 14- / 34- ENTER 15- + 35- ENTER 16- 2 36- * 17- + 37- CHS 18- x<>y 38- 1 19- e^x 39- + 20- ENTER 40- SQRT 41- GTO 00 Usage: Enter angle in radians ( 0 <= x <= pi ) R/S -> sin(x) x<>y -> cos(x) / -> tan(x) Examples: x | sin(x) | cos(x) | tan(x) | ------+-------------+-------------+-------------+ 3.14 | 0.001592545 |-0.999998732 |-0.001592547 | 3.02 | 0.121293236 |-0.992616719 |-0.122195439 | 2.50 | 0.598472141 |-0.801143618 |-0.747022290 | 2.00 | 0.909297427 |-0.416146836 |-2.185039869 | 1.65 | 0.996865028 |-0.079120890 |-12.59926467 | 1.58 | 0.999999647 |-0.009203545 |-108.6491891 | 1.57 | 0.999999683 | 0.000796324 | 1255.769712 | 1.50 | 0.997494987 | 0.070737197 | 14.10142097 | 1.00 | 0.841470986 | 0.540302303 | 1.557407735 | 0.50 | 0.479425548 | 0.877582557 | 0.546302504 | 0.05 | 0.049979231 | 0.998750257 | 0.050041770 | 0.00 | 0.000000000 | 1.000000000 | 0.000000000 | x |sin(x*pi/180)|cos(x*pi/180)|tan(x*pi/180)| ------+-------------+-------------+-------------+ 180.0 | 0.000000000 |-1.000000000 | 0.000000000 | 179.0 | 0.017452387 |-0.999847696 |-0.017455045 | 150.0 | 0.499999998 | 0.866025405 |-0.577350265 | 135.0 | 0.707106777 |-0.707106785 |-0.999999989 | 120.0 | 0.866025404 |-0.500000000 |-1.732050807 | 90.1 | 0.999998477 |-0.001745334 |-572.9552528 | 90.0 | 1.000000000 | 0.000000002 | 577350260.0*| 89.9 | 0.999998477 | 0.001745326 | 572.9581364 | 60.0 | 0.866025403 | 0.500000002 | 1.732050799 | 45.0 | 0.707106784 | 0.707106779 | 1.000000006 | 30.0 | 0.499999999 | 0.866025404 | 0.577350268 | 1.0 | 0.017452857 | 0.999847687 | 0.017455515 | (*) tan(90°) = oo pi = 3.141592654 Formulas: cos(x) ~ x^4/12 + (x^4/12)^2/140 - cosh(x) + 2 sin(x) = sqrt(1 - (cos(x))^2) cos(3*x) = cos(x)*(4*(cos(x))^2 - 3) More details at Mardi Gras Basic Trigs (HP-12C). HP 12c Platinum 001- 3 020- 1/x 002- / 021- + 003- ENTER 022- 2 004- ENTER 023- / 005- x^2 024- - 006- x^2 025- ENTER 007- 12/ 026- x^2 008- ENTER 027- 4 009- x^2 028- * 010- 1 029- 3 011- 4 030- - 012- 0 031- * 013- / 032- ENTER 014- + 033- x^2 015- 2 034- CHS 016- + 035- 1 017- x<>y 036- + 018- e^x 037- SQRT 019- ENTER 038- GTO 000 Examples: x | sin(x) | cos(x) | tan(x) | ------+-------------+-------------+-------------+ 3.14 | 0.001592628 |-0.999998732 |-0.001592630 | 3.02 | 0.121293239 |-0.992616719 |-0.122195442 | 2.50 | 0.598472143 |-0.801143617 |-0.747022294 | 2.00 | 0.909297427 |-0.416146837 |-2.185039863 | 1.65 | 0.996865028 |-0.079120889 |-12.59926479 | 1.58 | 0.999999646 |-0.009203543 |-108.6492026 | 1.57 | 0.999999683 | 0.000796327 | 1255.765641 | 1.50 | 0.997494987 | 0.070737202 | 14.10141994 | 1.00 | 0.841470985 | 0.540302306 | 1.557407725 | 0.50 | 0.479425539 | 0.877582562 | 0.546302490 | 0.05 | 0.049979169 | 0.998750260 | 0.050041708 | 0.00 | 0.000000000 | 1.000000000 | 0.000000000 | x |sin(x*pi/180)|cos(x*pi/180)|tan(x*pi/180)| ------+-------------+-------------+-------------+ 180.0 | 0.000000000 |-1.000000000 | 0.000000000 | 179.0 | 0.017452383 |-0.999847696 |-0.017455041 | 150.0 | 0.499999997 | 0.866025406 |-0.577350264 | 135.0 | 0.707106780 |-0.707106785 |-1.000000003 | 120.0 | 0.866025404 |-0.500000000 |-1.732050806 | 90.1 | 0.999998477 |-0.001745329 |-572.9571280 | 90.0 | 1.000000000 |-2.684678-10 |-3724840447* | 89.9 | 0.999998477 | 0.001745328 | 572.9572886 | 60.0 | 0.866025404 | 0.500000000 | 1.732050808 | (*) tan(90°) = oo ``` Edited by mistake. No changes. Edited: 1 Apr 2013, 2:48 p.m. after one or more responses were posted

 Re: Easter Sunday Basic Trigs (HP-12C)Message #2 Posted by Namir on 31 Mar 2013, 8:53 a.m.,in response to message #1 by Gerson W. Barbosa Gerson, Thank you soooo much for the listing and its algorithm. This has come at a time when I am also studying the algorithms than can be used to calculate the sine function. So I have added your method to the list. The accuracy results of your method are very impressive. So far your algorithm is at the top of the hit parade, so to speak! Using the trig identities for cos(3x) and sin(2x) I can use your method to cover a wide range of angles WHILE STILL maintaining very low errors! Namir Edited: 31 Mar 2013, 8:54 a.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #3 Posted by Namir on 31 Mar 2013, 10:18 a.m.,in response to message #1 by Gerson W. Barbosa It seems the presence of the cosh(x) function in your formula for calculating cos(x) is unusual and yet probably renders the formula stable enough to yield good results. My approach has been to find and use polynomials (either regular ones or rational ones like with the Pade approximants) and avoid as much as possible relying on functions like exp(x), ln(x), and so on. The Pade approximants yield rational polynomials (of a while variety of orders to pick and choose from) that generally offer stable results, especially when the approximated function has a Taylor series with consecutive terms that alternate in signs causing the series to converge very slowly. Such slow convergence also requires a large number of terms to achieve small errors over a significant range of x values. Edited: 31 Mar 2013, 10:19 a.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #4 Posted by Gerson W. Barbosa on 31 Mar 2013, 11:50 a.m.,in response to message #3 by Namir Hello Namir, I am glad you have liked this approximation. I find it particularly suitable for the HP-12C, since it has e^x and divide by 12 is available as a single instruction. Even with only the term x^4/12 it is good enough for practical purposes in the range [-pi/4..pi/4]: plot cos(x) - (x^4/12 - cosh(x) + 2), x=-pi/4..pi/4 (WolframAlpha) Adding a second term significantly improves the approximation: One additional term would perhaps allow for the evaluation of the function in the range [-pi/2..pi/2] to 10 places without range reduction. Best regards, Gerson. Edited: 31 Mar 2013, 1:40 p.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #5 Posted by Namir on 31 Mar 2013, 1:42 p.m.,in response to message #4 by Gerson W. Barbosa Adding the cubic term does improve accuracy a bit, and I welcome that!!! Thanks for adding the plots!!!! I have also tested other approximations for sin(x) that I found on the web. You methods puts them all to shame!! Namir Edited: 31 Mar 2013, 1:44 p.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #6 Posted by Gerson W. Barbosa on 31 Mar 2013, 1:59 p.m.,in response to message #5 by Namir Thanks, but please keep in mind that this only works when we have ex readily available, otherwise the computation of ex alone would not compensate at all. Gerson.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #7 Posted by Namir on 1 Apr 2013, 7:21 a.m.,in response to message #6 by Gerson W. Barbosa I am thinking about expanding cosh(x) into a Taylor series polynomial (or even better yet a Pade approximant rattional polynomials) so that the whole evaluation of cos(x) (and then sin(x)) relies on basic operations only. Namir

 Re: Easter Sunday Basic Trigs (HP-12C)Message #8 Posted by Namir on 1 Apr 2013, 8:05 a.m.,in response to message #6 by Gerson W. Barbosa Using the following Pade approximation for cosh(x) works well: ```cosh(x) = (39251520 + 18471600 x^2 + 1075032 x^4 + 14615 x^6)/(39251520 - 1154160 x^2 + 16632 x^4 - 127 x^6) ``` The calculated cos and sin have a very good accuracy from 0 to 89 degrees. At 90 degrees this (and many other) approximations suffer! Namir Edited: 1 Apr 2013, 1:53 p.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #9 Posted by Thomas Klemm on 31 Mar 2013, 4:39 p.m.,in response to message #3 by Namir Quote: especially when the approximated function has a Taylor series with consecutive terms that alternate in signs causing the series to converge very slowly. Maybe I do not understand you correctly, but why should an alternating series converge slowly? On the contrary: in alternating series, the Euler transformation can be used for convergence acceleration. Kind regards Thomas Edited: 1 Apr 2013, 9:15 a.m. after one or more responses were posted

 Re: Easter Sunday Basic Trigs (HP-12C)Message #10 Posted by Namir on 1 Apr 2013, 8:10 a.m.,in response to message #9 by Thomas Klemm Maybe you are correct. I will check it. Namir

 Re: Easter Sunday Basic Trigs (HP-12C)Message #11 Posted by Thomas Klemm on 31 Mar 2013, 3:54 p.m.,in response to message #1 by Gerson W. Barbosa May I suggest the following change: ```16- x<>y 17- e^x 18- ENTER 29- 1/x 20- + 21- 2 22- / 23- 2 ; or LSTx 24- - 25- - ``` The rationale behind this change is that 2 - cosh(x) < 1 for x # 0, thus we gain one digit. For small values of x this makes a difference: ``` x | sin(x) | cos(x) | tan(x) | ------+-------------+-------------+-------------+ 0.05 | 0.049979164 | 0.998750261 | 0.050041703 | ``` Kind regards Thomas Edited: 31 Mar 2013, 4:00 p.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #12 Posted by Gerson W. Barbosa on 31 Mar 2013, 4:46 p.m.,in response to message #11 by Thomas Klemm Thanks for the improvement! I've just tried the following on the fast HP-12C+: ```01 STO 0 02 0 03 STO 1 04 STO 2 05 RCL 0 06 RCL 1 07 y^x 08 LASTx 09 n! 10 / 11 STO+ 2 12 4 13 STO+ 1 14 2 15 0 16 RCL 1 17 x<=y? 18 GTO 05 19 RCL 2 20 2 21 * 22 RCL 0 23 e^x 24 ENTER 25 1/x 26 + 27 2 28 / 29 - 30 ENTER 31 ENTER 32 * 33 CHS 34 1 35 + 36 SQRT 37 GTO 00 For your example, I get x | sin(x) | cos(x) | tan(x) | ------+-------------+-------------+-------------+ 0.05 | 0.049979164 | 0.998750261 | 0.050041736 | ``` With 20 in lines 14 and 15 (6 terms of the Taylor expansion) the valid range for cos(x) appears to go from -pi to pi without range reduction (this have to be checked). The hp 12 Platinum might give more accurate results, but I don't know if it will be fast enough. There are many rounding errors involved, but perhaps your method should apply here. I have to leave now, so I'll see this later. Cheers, Gerson. P.S.: There was a typo in line 19 (RCL 1 instead of RCL 2); It takes about four seconds on the hp 12 Platinum: ``` x | sin(x) | cos(x) | tan(x) | ------+-------------+-------------+-------------+ 0.05 |0.04997916917| 0.9987502604|0.05004170837| ``` Formula: Edited: 31 Mar 2013, 7:36 p.m.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #13 Posted by Namir on 31 Mar 2013, 9:29 p.m.,in response to message #12 by Gerson W. Barbosa Ah! I was going to ask you for the equation that generates the polynomial part. Namir

 Re: Easter Sunday Basic Trigs (HP-12C)Message #14 Posted by Gerson W. Barbosa on 1 Apr 2013, 12:21 a.m.,in response to message #13 by Namir This is better explained in this thread, message #5: For testing purpose, the following should give at least 10 correct digits on the HP-50g, in the range [-pi..pi]. ```%%HP: T(3)A(R)F(.); \<< \-> x \<< '2*\GS(k=0,5,x^(4*k)/(4*k)!)-COSH(x)' EVAL \>> \>> ``` Gerson.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #15 Posted by Gerson W. Barbosa on 1 Apr 2013, 9:54 p.m.,in response to message #11 by Thomas Klemm Thomas, I'll accept your suggestion. Listings and examples below. The results comparisons have been made against the HP-15C. Cheers, Gerson. ```HP-12C 01- 3 21- 2 02- / 22- / 03- ENTER 23- LSTx 04- ENTER 24- - 05- 4 25- - 06- y^x 26- ENTER 07- 12/ 27- ENTER 08- ENTER 28- * 09- ENTER 29- 4 10- * 30- * 11- 1 31- 3 12- 4 32- - 13- 0 33- * 14- / 34- ENTER 15- + 35- ENTER 16- x<>y 36- * 17- e^x 37- CHS 18- ENTER 38- 1 19- 1/x 39- + 20- + 40- SQRT 41- GTO 00 Usage: Enter angle in radians ( 0 <= x <= pi ) R/S -> sin(x) x<>y -> cos(x) / -> tan(x) Examples: x | sin(x) | cos(x) | tan(x) | ------+------------------+------------------+-------------------+ 3.14 | 0.001592545(653) |-0.999998732 |-0.001592547(655) | 3.02 | 0.121293238(55) |-0.992616719(7) |-0.122195441(59) | 2.50 | 0.598472142(4) |-0.801143617(6) |-0.747022293(7) | 2.00 | 0.909297427 |-0.416146836(7) |-2.185039866(3) | 1.65 | 0.996865029 |-0.079120888(9) |-12.59926494(79) | 1.58 | 0.999999647 |-0.009203547(3) |-108.6491585(2036) | 1.57 | 0.999999683 | 0.000796325(7) | 1255.768346(5591) | 1.50 | 0.997494987 | 0.070737197(202) | 14.10142097(1995) | 1.00 | 0.841470986(5) | 0.540302304(6) | 1.557407731(25) | 0.50 | 0.479425542(39) | 0.877582560(2) | 0.546302495(0) | 0.05 | 0.049979164(9) | 0.998750261(0) | 0.050041703(8) | 0.00 | 0.000000000 | 1.000000000 | 0.000000000 | x | sin(x*pi/180) | cos(x*pi/180) | tan(x*pi/180) | ------+------------------+------------------+-------------------+ 180.0 | 0.000002000(0000)|-1.000000000 | 0.000002000(0000) | 179.0 | 0.017452392(406) |-0.999847695 |-0.017455051(65) | 150.0 | 0.499999997(50..)|-0.866025406(4) |-0.577350265(9) | 135.0 | 0.707106778(81) |-0.707106784(1) |-0.999999989(100..)| 120.0 | 0.866025404 |-0.500000000 |-1.732050810(08) | 90.1 | 0.999998477 |-0.001745333(28) |-572.9558211(72134)| 90.0 | 1.000000000 | 0.000000002(0) | 1154700538 ( +oo )| 89.9 | 0.999998477 | 0.001745327(8) | 572.9575675(2134) | 60.0 | 0.866025405(4) | 0.499999999(50..)| 1.732050814(08) | 45.0 | 0.707106781 | 0.707106782(1) | 0.999999999(10..) | 30.0 | 0.500000007(0) | 0.866025400(4) | 0.577350280(69) | 1.0 | 0.017452793(406) | 0.999847688(95) | 0.017455452(065) | pi = 3.141592654 HP 12c Platinum 001- 3 020- 2 002- / 021- / 003- ENTER 022- LSTx 004- ENTER 023- - 005- x^2 024- - 006- x^2 025- ENTER 007- 12/ 026- x^2 008- ENTER 027- 4 009- x^2 028- * 010- 1 029- 3 011- 4 030- - 012- 0 031- * 013- / 032- ENTER 014- + 033- x^2 015- x<>y 034- CHS 016- e^x 035- 1 017- ENTER 036- + 018- 1/X 037- SQRT 019- + 038- GTO 000 Examples: x | sin(x) | cos(x) | tan(x) | ------+------------------+------------------+-------------------+ 3.14 | 0.001592628(53) |-0.999998732 |-0.001592630(55) | 3.02 | 0.121293239(55) |-0.992616719(7) |-0.122195442(59) | 2.50 | 0.598472143(4) |-0.801143617(6) |-0.747022294(7) | 2.00 | 0.909297427 |-0.416146837 |-2.185039862(3) | 1.65 | 0.996865028(9) |-0.079120889 |-12.59926479 | 1.58 | 0.999999646(7) |-0.009203543 |-108.6492029(36) | 1.57 | 0.999999683 | 0.000796327 | 1255.765628(591) | 1.50 | 0.997494987 | 0.070737202 | 14.10141994(5) | 1.00 | 0.841470985 | 0.540302306 | 1.557407725 | 0.50 | 0.479425539 | 0.877582562 | 0.546302490 | 0.05 | 0.049979169 | 0.998750260 | 0.050041708 | 0.00 | 0.000000000 | 1.000000000 | 0.000000000 | x | sin(x*pi/180) | cos(x*pi/180) | tan(x*pi/180) | ------+------------------+------------------+-------------------+ 180.0 | 0.000000000 |-1.000000000 | 0.000000000 | 179.0 | 0.017452382(406) |-0.999847696(6) |-0.017455041(65) | 150.0 | 0.499999997(50..)|-0.866025406(4) |-0.577350264(9) | 135.0 | 0.707106780(1) |-0.707106782(1) |-0.999999997(10..) | 120.0 | 0.866025404 |-0.500000000 |-1.732050805(8) | 90.1 | 0.999998477 |-0.001745329(8) |-572.9571394(2134) | 90.0 | 1.000000000 |-0.00000000026(+0)|-3849001795 ( +oo )| 89.9 | 0.999998477 | 0.001745328 | 572.9572858(134) | 60.0 | 0.866025404 | 0.500000000 | 1.732050808 | 45.0 | 0.707106781 | 0.707106781 | 1.000000000 | 30.0 | 0.500000000 | 0.866025404 | 0.577350269 | 1.0 | 0.017452408(6) | 0.999847695 | 0.017455067(5) | pi = 3.141592654 ```

 Re: Easter Sunday Basic Trigs (HP-12C)Message #16 Posted by BShoring on 31 Mar 2013, 5:54 p.m.,in response to message #1 by Gerson W. Barbosa Thank you for this nice program. It also works on the HP-38E and HP-38C which happens to be my favorite calculator, and which was the predeccessor to the HP-12C.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #17 Posted by Gerson W. Barbosa on 31 Mar 2013, 7:56 p.m.,in response to message #16 by BShoring Which do you have, the HP-38E or HP-38C? There is another trigs program on the software library, using another approach (minimax polynomial approximation). It's very inconvenient on the HP-38E however (99 steps and 7 constants in the registers). Regards, Gerson.

 Re: Easter Sunday Basic Trigs (HP-12C)Message #18 Posted by BShoring on 1 Apr 2013, 1:31 a.m.,in response to message #17 by Gerson W. Barbosa Gerson, I had the C, for 20 great years of heavy use. Died about 10 years ago as has my HP41CV. Fortunately I have a 38C emulator (and many others) that works perfectly. Thanks, Bob

 Question about COSH(X) termMessage #19 Posted by Namir on 1 Apr 2013, 1:55 p.m.,in response to message #1 by Gerson W. Barbosa Gerson, How did the cosh(x) term end up in the approximation for cos(x)???? A very curious Namir

 Re: Question about COSH(X) termMessage #20 Posted by Gerson W. Barbosa on 1 Apr 2013, 3:14 p.m.,in response to message #19 by Namir Just sum the respective Taylor series together and then isolate cos x: $\cosh x = 1 + \frac{x^{2}}{2!} + \frac{x^{4}}{4!} + \frac{x^{6}}{6!}+ \cdots$ $\cos x = 1 - \frac{x^{2}}{2!} + \frac{x^{4}}{4!} - \frac{x^{6}}{6!}+ \cdots$ $\cosh x+\cos x= 2\cdot \left ( 1 + \frac{x^{4}}{4!} + \frac{x^{8}}{8!} + \cdots \right )$ $\cos x= 2\cdot \left ( 1 + \frac{x^{4}}{4!} + \frac{x^{8}}{8!} + \cdots \right ) - \cosh x$ Regards, Gerson. Edited to fix a typo and to correct a mistake in the fourth paragraph, per Thomas Klemm's observation below Edited: 4 Apr 2013, 1:29 p.m. after one or more responses were posted

 Re: Question about COSH(X) termMessage #21 Posted by Namir on 1 Apr 2013, 4:13 p.m.,in response to message #20 by Gerson W. Barbosa Very elegant and very simple!!! :-) Namir

 Re: Question about COSH(X) termMessage #22 Posted by Les Koller on 1 Apr 2013, 9:50 p.m.,in response to message #21 by Namir That's the way I like my math!

 Re: Question about COSH(X) termMessage #23 Posted by Gerson W. Barbosa on 1 Apr 2013, 10:16 p.m.,in response to message #21 by Namir I fixed a missing multiplication by 2 in the fourth line soon after posting, but forgot to do the same on the third line. Sorry for the mistake! It's been corrected now! Edited: 4 Apr 2013, 1:42 p.m.

 Re: Question about COSH(X) termMessage #24 Posted by Namir on 1 Apr 2013, 4:20 p.m.,in response to message #20 by Gerson W. Barbosa One can use a similar approach for sin(x): ```sin(x) = x (2 + y/60 + y^2/181440 + y^3/3113510400 + y^4/177843714048000 + y^5/25545471085854720000 + y^6/7755605021665492992000000 + y^7/4420880996869850977271808000000) - sinh(x) Where y = x^4 ``` Namir Edited: 1 Apr 2013, 4:21 p.m.

 Re: Question about COSH(X) termMessage #25 Posted by Gerson W. Barbosa on 2 Apr 2013, 7:23 p.m.,in response to message #24 by Namir Which of course works nicely :-)

 Re: Question about COSH(X) termMessage #26 Posted by Thomas Klemm on 4 Apr 2013, 11:41 a.m.,in response to message #20 by Gerson W. Barbosa Quote: $\cosh x + \cos x = 1 + \frac{x^{4}}{4!} + \frac{x^{8}}{8!} + \cdots$ The factor 2 is missing: $\cosh x + \cos x=2\cdot(1+\frac{x^{4}}{4!}+\frac{x^{8}}{8!}+\cdots)$ But of course we still get the idea. Kind regards Thomas

 Re: Question about COSH(X) termMessage #27 Posted by Gerson W. Barbosa on 4 Apr 2013, 1:41 p.m.,in response to message #26 by Thomas Klemm The last line was right, nonetheless. The previous line has now been corrected, thanks! Cheers, Gerson.

 Re: Easter Sunday Basic Trigs (HP-17BII version)Message #28 Posted by Gerson W. Barbosa on 3 Apr 2013, 9:17 p.m.,in response to message #1 by Gerson W. Barbosa The following gives about 10 to 11 significant digits in the range [0..+/-pi], in case anyone wants to try. They should work in other HP-17B models as well. ```SIN=2*SIGMA(K:1:21:4:X^K/FACT(K))-(EXP(X)-EXP(-X))/2 COS=2*SIGMA(K:0:20:4:X^K/FACT(K))-(EXP(X)+EXP(-X))/2 TAN=(4*SIGMA(K:1:21:4:X^K/FACT(K))-EXP(X)+EXP(-X))/(4*SIGMA(K:0:20:4:X^K/FACT(K))-EXP(X)-EXP(-X)) X in radians. ```

 Re: Easter Sunday Basic Trigs (HP-12C)Message #29 Posted by Eddie W. Shore on 4 Apr 2013, 7:53 a.m.,in response to message #1 by Gerson W. Barbosa Gerson, Simple, elegant, and accurate (to at least 6 digits). Beautiful algorithm! Eddie

 Re: Easter Sunday Basic Trigs (HP-12C)Message #30 Posted by Gerson W. Barbosa on 4 Apr 2013, 2:19 p.m.,in response to message #29 by Eddie W. Shore Thanks, Eddie! Quote: accurate (to at least 6 digits) The next term in the Taylor series, 2*(x)^16/16!, would contribute with only 2e-13, at most (in the extremes of the [-pi..pi] range, when x = pi/3). The lost of accuracy is greater for the sine function (and tangent), because it is computed as sqrt(1 - cos2x). The lack of at least two guard digits is also responsible for many accumulated errors. Anyway, 6 digits are quite an improvement after almost seven centuries :-) "In 1342, Levi (ben Gerson) wrote On Sines, Chords and Arcs, which examined trigonometry, in particular proving the sine law for plane triangles and giving five-figure sine tables." (From Wikipedia) Cheers, Gerson.

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