[VA] SRC#004 Fun with Sexagesimal Trigs

02112019, 04:13 PM
Post: #1




[VA] SRC#004 Fun with Sexagesimal Trigs
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Hi, all: Welcome to my brand new SRC#004, this time commemorating that this is my 300^{th} post here so if I'm not mistaken I'll be granted the description "Senior Member" from now on. What a treat ! Tired of trigs in radians ? Wanna see some trigs in sexagesimal degrees ? Read on ! Details: If you're in the mood for a nice helping of awesome "sexagesimal" results go and try your hand at accurately evaluating the following trig expressions, either manually or else by writing a short bit of RPN/RPL/71BASIC/HPPL code for your preferred HP calculator (not Excel, Matlab, Mathematica, Python, Java, Haskell, C/C++, Wolfram Alpha, etc., there are many other forums/threads for that), namely: \[ A = (\sqrt{3}\;+\;tan\;1º)\;(\sqrt{3}\;+\;tan\;2º)\;...\;(\sqrt{3}\;+\;tan\;29º) \] \[ B = \frac{1}{sin\;45º \; sin\;46º} +\frac{1}{sin\;47º \; sin\;48º} \; + \;...\; + \; \frac{1}{sin\;133º \; sin\;134º} \] \[ C = \left(1  \frac{cos\;61º}{cos\;1º}\right) \; \left(1  \frac{cos\;62º}{cos\;2º}\right) \; ... \; \left(1  \frac{cos\;119º}{cos\;59º}\right) \] \[ D = \left(1\frac{1}{tan\;1º}\right)\;\left(1\frac{1}{tan\;2º}\right)\; ...\; \left(1\frac{1}{tan\;44º}\right) \] \[ E = \left(2\;cos\;2^2º\frac{1}{cos\;2^2º}\right)\;\left(2\;cos\;2^3º\frac{1}{cos\;2^3º}\right)\;...\;\left(2\;cos\;2^{25}º\frac{1}{cos\;2^{25}º}\right) \] Once you've succeeded in accurately evaluating them you should attempt to identify the results that aren't immediately obvious (i.e.: if you get something like 1.7320508.. you should identify it as \(\sqrt{3}\)), which will be useful to gauge the accuracy obtained by comparing what you got with the exact results, benchmarklike. You must not use anything other than your intuition and the help of your trusty HP calculator for the identification (in particular give the Internet a miss) but those of you using HP calcs with CAS might want to check if your CAS will produce the exact results at once or if at least it will simplify them to something much .. well, simpler ! Let's see your code, results and comments (try not to spoil early the fun for others), I will post mine within a few days. V. . 

02112019, 07:55 PM
Post: #2




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
(02112019 04:13 PM)Valentin Albillo Wrote: You must not use anything other than your intuition and the help of your trusty HP calculator for the identification... So the use of your great IDENTIFY program is perfectly legal ? :) JF 

02112019, 09:26 PM
Post: #3




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
Amazing expressions !
Programming (especially on the 71) is immediate  no need to post it  , but the identification of the B value stopped me for a while. JF 

02112019, 09:51 PM
(This post was last modified: 02122019 01:37 AM by Gerson W. Barbosa.)
Post: #4




RE: [VA] SRC#004 Fun with Sexagesimal Trigs  
02122019, 03:37 AM
(This post was last modified: 02142019 02:39 AM by Albert Chan.)
Post: #5




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
(02112019 09:26 PM)JF Garnier Wrote: the identification of the B value stopped me for a while. Here is a good way to estimate B. Middle term angle is around 90°, any angles bigger than that can be used to fill the "holes": Example, 1/(sin(133°)sin(134°)) = 1/(sin(47°)sin(46°)) So, B = 1/(sin(45°)sin(46°)) + 1/(sin(46°)sin(47°)) + ... + 1/(sin(89°)sin(90°)) I remember derivative of tan(x) is sec(x)^2 = 1/cos(x)^2 So, change all the sines to cosines, angles goes from 0° to 45° The x's are in degree, so need to scale the area, like this: sum ~ (180/Pi) * integrate(sec(x)^2, x, 0, Pi/4) = (180/Pi) * (1  0) = 180/Pi Actual sum is not exactly like this, but should be close. My guess for true sum is 1/sin(1°), but to prove it is hard ... 

02122019, 08:05 AM
(This post was last modified: 02122019 08:37 AM by JF Garnier.)
Post: #6




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
(02112019 09:26 PM)JF Garnier Wrote: Programming (especially on the 71) is immediate  no need to post it  Well, straightforward programming is indeed immediate and enough to get an idea of the results, but it is possible to do slightly better "in accurately evaluating them" Let's see on value A. Straightforward programming: >A=1 @ FOR I=1 TO 29 @ A=A*(SQR(3)+TAN(I)) @ NEXT I @ DISP A 536870912.011 The rounding error on SQR(3), accumulated on 29 successive iterations introduces a systematic bias. We can reduce this effect by factoring SQR(3) and evaluating SQR(3)^29 directly: >A=1 @ FOR I=1 TO 29 @ A=A*(1+TAN(I)/SQR(3)) @ NEXT I @ A=A*3^14*SQR(3) @ DISP A 536870912.002 This gives us more confidence in identifying it to a certain simple integer expression. JF 

02122019, 09:50 AM
(This post was last modified: 02122019 09:50 AM by Gerson W. Barbosa.)
Post: #7




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
(02122019 08:05 AM)JF Garnier Wrote: The rounding error on SQR(3), accumulated on 29 successive iterations introduces a systematic bias. Right in between: « 1 1 29 FOR i i DUP + SIN LASTARG COS 1 + / 3 √ + * NEXT » EVAL > 536870912.006 

02122019, 12:14 PM
Post: #8




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
Prove A = 2^29 = 536870912:
Checking the edges, using shorthand t# = tan(#°): tan(A°+B°) = (tA + tB) / (1  tA tB) (t60 + tA) (t60 + tB), where A+B=30° = t60^2 + t60*(tA + tB) + tA tB = t60^2 + t60*t30*(1  tA tB) + tA tB = 3 + 1  tA tB + tA tB = 2^2 t15 = tan(45°  30°) = (t45  t30) / (1 + t45 t30) = (1  1/√3) / (1 + 1/√3) = (√3  1) / (√3 + 1) = (√3  1)^2 / (3  1) = (3 + 1  2*√3) / 2 > t15 = 2  √3 > center = t60 + t15 = 2 14 pairs of edges and 1 center, all can considered value of 2, thus A = 2^29 

02122019, 01:23 PM
Post: #9




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
(02122019 12:14 PM)Albert Chan Wrote: Prove A = 2^29 = 536870912: A is the only one I had trouble with because at first I had wrongly programmed it as a sum instead of a product. When I notice my mistake and finally got the correct value, I simply computed its base2 logarithm in order to check it was a power of two. But only because I had identified D already. For whatever reason I decided to check the product of the first and last terms: (1  1/tan1°)*(1  1/tan44°) = 1.99999999997 That’s 2 to me, so I just did 2^22 = 4194304 which “matched” 4194303.99965, the value my D program returned, and I gave it no further thought. I do appreciate, however, your efforts in going deeper into the problem and providing a proof. Gerson. 

02122019, 02:11 PM
Post: #10




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
(02122019 12:14 PM)Albert Chan Wrote: Prove A = 2^29 = 536870912: Great! With the same method (and notations), it's easy to prove D = 2^22: tan(A°+B°) = (tA + tB) / (1  tA tB) (1  1/tA) (1  1/tB), where A+B=45° = 1  (1/tA + 1/tB) + 1/(tA tB) = 1  (tA + tB) / (tA tB) + 1 / (tA tB) = 1  t45 (1  tA tB) / (tA tB) + 1 / (tA tB) = 1  (1 / (tA tB)  1) + 1 / (tA tB) = 2 JF 

02122019, 04:39 PM
(This post was last modified: 02122019 04:41 PM by Albert Chan.)
Post: #11




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
Prove C = 1:
Using shorthand c(#) = c# = cos(#°), s(#) = s# = sin(#°) C = (1  c61/c1)(1  c62/c2) ... (1  c119/c59) center = (1 + c90/c30) = (1 + 0/c30) = 1 Check the edges, each pair P had the form: = (1  c(90x)/c(30x)) * (1  c(90+x)/c(30+x)) = (1  sx / c(30x)) * (1 + sx / c(30+x)) To simplify P, we need these identities: cos(A+B) = cos(A)cos(B) − sin(A)sin(B) cos(A−B) = cos(A)cos(B) + sin(A)sin(B) Removing the annoying denominator, let k = c(30x) * c(30+x) k P = (c(30+x)  sx) * (c(30x) + sx) = k + sx^2 + sx * (c(30+x)  c(30x)) = k + sx^2 + sx * (2 s(30) sx) = k + sx^2 − sx^2 = k > P = 1 All factors can considered value of 1, thus C = 1 

02122019, 05:58 PM
Post: #12




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
Prove E = 1:
This one is easy. Just do the first term, using shorthand c(#) = c# = cos(#°) (2 c4  1/c4) = (2 c4^2  1) / c4 = c8 / c4 Numerator and denominator for everything cancelled out, except c(2^26)/c(4) c(2^26) = c(2^26 mod 360) = c184 = c4 > E = c4/c4 = 1 

02142019, 03:33 AM
Post: #13




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
Solutions with RPL. These programs are designed to not be flexible. Only to solve the problem.
Code: Spoilers for A Code: Spoilers for B Code: Spoilers for C Code: Spoilers for D Code: Spoilers for E Fun programming. 

02142019, 01:23 PM
(This post was last modified: 08062019 11:44 AM by Albert Chan.)
Post: #14




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
B = 1/(s45s46) + 1/(s47s18) + ... 1/(s89s90) + 1/(s91s92) + ... + 1/(s133s134)
= 1/(c44c45) + 1/(c42c43) + ... 1/(c0c1) + 1/(c1c2) + ... + 1/(c43c44) = 1/(c0c1) + 1/(c1c2) + 1/(c2c3) + ... + 1/(c44c45) Proof below statement by induction. If success, it proved B = tan(45°) / sin(1°) = 1/sin(1°) sum(1/(cos(k°)*cos((k+1)°)), k=0 to n1) = tan(n°) / sin(1°) For n=1, 1/(c0c1) = 1/c1 = tan(1°) / sin(1°) Assume this work for n=k, add 1 more term, we got: tan(k°) / sin(1°) + 1/(ck c(k+1)) = (sk c(k+1) + s1) / (s1 ck c(k+1)) Since s1 = s((k+1)  k) = s(k+1) ck  c(k+1) sk, we got: Sum of k+1 terms = (s(k+1) ck) / (s1 ck c(k+1)) = tan((k+1)°) / sin(1°) QED Update: above general formula work in any angle unit, not just degrees. 

02242019, 06:17 PM
(This post was last modified: 02242019 07:15 PM by Valentin Albillo.)
Post: #15




RE: [VA] SRC#004 Fun with Sexagesimal Trigs
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Hi, all: A short proof of the evaluation of B:\[ B = \frac{1}{sin\;45º \; sin\;46º} +\frac{1}{sin\;47º \; sin\;48º} \; + \;...\; + \; \frac{1}{sin\;133º \; sin\;134º} = \frac{1}{sin\;1º} \]1) First, we multiply both sides by sin 1º: \[ \frac{sin \;1º}{sin\;45º \; sin\;46º} +\frac{sin \;1º}{sin\;47º \; sin\;48º} \; + \;...\; + \; \frac{sin \;1º}{sin\;133º \; sin\;134º} = \frac{sin \;1º}{sin\;1º} = 1 \]2) Now we use the identity \[ \frac{sin((k + 1)º  kº)}{sin\;kº\;sin(k + 1)º} = cot\;kº  cot(k + 1)º \]which transforms the lefthand side into this: \[ cot\; 45º  cot\; 46º + cot\; 47º  cot\; 48º +···+ cot\; 133º  cot\; 134º \]3) Then we reorder the terms in the sum like this: \[ cot \;45º  (cot \;46º + cot \;134º) + (cot \;47º + cot \;133º)  ··· + (cot \;89º + cot \;91º)  cot \;90º \]4) All the terms inside the parentheses cancel out because they feature supplementary angles ( cot Nº + cot (180ºNº) = 0 ), so the expression reduces to: \[ cot \;45º  cot \;90º = 1 0 = 1 \] Q.E.D. Thanks for your interest and have a nice weekend. V . 

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