[sf-lug] py class: need math help!

[Charles-Henri Gros]

Alex Kleider wrote:
> --- On Sun, 10/5/08, jim <jim at well.com> wrote:
> 
>>    so what is the goal? 
>>
>>
>>
>>
>> On Sun, 2008-10-05 at 09:47 -0700, Alex Kleider wrote:
>>> I need some help with what seems to be elementary
>> math/trig:
>>> Take a pencil and piece of paper and try to stay with
>> me:
>>> We start at C for center of circle and based on that
>> center 
>>> draw an arc of radius r from A to B such that the
>> angle ACB is equal to twice theta
>>> bisect our angle with a line from C to D at the
>> midpoint of the arc.
>>> it intersects AB at E
>>> Now I've been assuming that triangles DEB and BEC
>> were similar and therefore
>>> knowing ED and EB I was solving for CB (the radius.)
>>> i.e : tan theta = ED / EB
>>>    and radius = CB = EB/sin theta
>>>
>>> This is my attempt to solve the next series of
>> problems.
>>> I'd appreciate any help.
>>>
> I'm sorry for not being clear :
> the goal is :
> if one wants ED and EB to be specific lengths (say 20 and 50 respectively)
> How to calculate the radius and the angle to give this.

As per my previous e-mail, ED = EB tan (theta/2). This gives you theta
theta = 2 atan(ED/EB)

r = CE + ED
CE = EB / tan theta
r = EB / tan theta + ED

This gives you r

-- 
Charles-Henri