[pstricks] Solving equations with pstricks (draw one-thid of an angle)

[Christoph Bersch]

On 22.05.2012 10:03, Plamen Tanovski wrote:
>
> I need to draw an one-third of an angle (\theta)
>
> To do so, I have to find the points E and D, so, that
>
> - E is on the circle OX
>
> - D is on the line BO
>
> - DE = OE = OX = r
>
> - X, E, D are on the same line
>
> I've looked at pst-eucl, but I can't see any way to find D and E.

Here is a suggestion, which needs some finetuning, but gives the 
requested points:

\documentclass{article}
\usepackage{pst-eucl}
\begin{document}
\def\mytheta{70\space}
\begin{pspicture}[showgrid](-5,0)(5,5)
   \pstGeonode(0,0){O}(-3,0){B}(3,0){Y}
% alternative \pstGeonode(3.5;110){A}
   \pstGeonode(! 180 \mytheta sub dup cos 3.5 mul exch sin 3.5 mul){A}
   \pstCircleOA{O}{B}
   \pstLineAB{O}{A}
   \pstInterLC{O}{A}{O}{Y}{X1}{X2}
   \nodexn{(X2)+(! \mytheta 3 div neg dup cos exch sin)}{X2'}
   \pstInterLC{X2}{X2'}{O}{Y}{E1}{E2}
   \pstInterLL{X2}{X2'}{O}{Y}{D}
   \pstLineAB{X2}{D}
   \pstLineAB{B}{D}
\end{pspicture}
\end{document}

Christoph