20171109, 18:43  #1 
Mar 2016
3×137 Posts 
angle bisection
A peaceful day for all,
a, b, c element N are known, where a, b, c build a pyth. trippel with a^2+b^2=c^2 tan (alpha)=a/b is there a way to calculate tan (alpha/2) without using the angle ? if not, how accurate i have to choose alpha to get a good result / the rational number of tan (alpha/2) ? Thanks in advance, if you give me a hint. Greetings from the primes Bernhard 
20171109, 18:53  #2 
"Robert Gerbicz"
Oct 2005
Hungary
2×3×263 Posts 

20171109, 20:05  #3 
"Rashid Naimi"
Oct 2015
Remote to Here/There
2288_{10} Posts 
To state the obvious the half tenant of alpha goes from
1/2 of the tan (alpha) for alpha=0° To 1 for alpha=90° So to get a good result for alpha=1°, just divide the tangent by 2 And for alpha= 89° Calculate the arctan With very little accuracy, Divide by 2 and calculate the tangent which should be very close to 1. Last fiddled with by a1call on 20171109 at 20:07 
20171109, 20:56  #4 
Feb 2005
Bristol, CT
3^{3}·19 Posts 
Where a, b, c build a pyth. trippel with a^2+b^2=c^2
tan (alpha)=a/b Code:
tan(alpha/2)=(cb)/a 
20171109, 22:16  #5 
Feb 2017
Nowhere
2×2,999 Posts 

20171112, 20:10  #6 
"Rashid Naimi"
Oct 2015
Remote to Here/There
2^{4}×11×13 Posts 
I have been thinking about this topic and find it quite interesting.
For a tangent in the range of 45° to 90° (1 to ∞), the half tangent ranges from (0.41 to 1). You could think of this in many different ways. For example as an infinite increase in precision. Or, since bisecting an angle is s constructible process (it can be done using a compass and a straight edge), it is conceivable to have mechanical machine which with a theoretical 0 thickness parts can infinity magnify a force. Of course in practice the magnification will be limited by the >0 thickness of the parts. I haven't been able to think of an electronic equivalent but it could exist and would be quite interesting, at least in a theoretical sense. Last fiddled with by a1call on 20171112 at 20:12 
20171113, 12:15  #7 
"Rashid Naimi"
Oct 2015
Remote to Here/There
8F0_{16} Posts 
I did some more thinking.
A similar concept would be a bow with infinity non stretchable string. Such a (theoretical) string would exert a force to the bow that is infinite times of any pulling force applied to it at t0. However the gain would very quickly drop to a very low finite value exponentially, past t0. 
20171113, 12:33  #8 
Aug 2002
Buenos Aires, Argentina
2·17·43 Posts 

20171113, 16:24  #9  
Feb 2017
Nowhere
2×2,999 Posts 
Quote:
In any event, a theoretically more satisfactory approach, applicable to dividing an angle by any positive integer, is to use the multipleangle formulas to get a polynomial equation for the required trig function. In the case of the tangent, let t = tan(\theta). Then, for k a positive integer, may be expressed as Im(1+i*t)^k/Re(1 + i*t)^k. Setting this rational expression equal to a given value for gives a polynomial for t = . The zeroes of the polynomial are , j = 0 to k1. In the case k = 2, the rational expression is 2t/(1  t^2). 

20171116, 19:54  #10 
Mar 2016
3·137 Posts 
Thanks a lot for these informations.
There is a question which follows immediately: If a, b, c element N and a² + b² = c² you can calculate tan (alpha) and tan (alpha/2) Is it possible to transform the tan (alpha/2) into a pyth. trippel with a*, b*, c* I thought that a*, b*, c* should be element N again, Example a=7, b=24, c=25 tan (alpha/2)=(cb)/a=1/7 (very elegant solution! ) But 1²+7²=50 so that c=sqrt (50) and c is not element N On the other hand i thought that the pyth trippel form a group. Somewhere there is a logical mistake. Would be nice, if someone could give a hint. Greetings from the pyth. trippel Bernhard 
20171116, 20:27  #11 
Dec 2012
The Netherlands
5·353 Posts 
We gave a complete parametrization of all primitive Pythagorean triples in the Number Theory discussion group here:
http://www.mersenneforum.org/showthread.php?t=21850 
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