# [pstricks] tangent to \psellipse or \pscircle

Patrick Drechsler patrick at pdrechsler.de
Tue Oct 30 00:16:46 CET 2007

Hi,

what is the best way to draw a tangent to \psellipse or \pscircle at
certain coordinates? And how does one retreive these coordinates?

--8<---------------cut here---------------start------------->8---
\documentclass{article}
\usepackage{pstricks}
\begin{document}
\begin{pspicture}[showgrid=true](-3,-3)(3,3)
\psdot(0,0)
\psellipse(0,0)(3,1.5)%
\psset{linewidth=0.5pt,linecolor=gray,linestyle=dashed}
\psline(0,0)(3,0)
%% How to draw a tangent at X=2 for Y>0?
%% ??
%% How do I retreive the X and Y coordinate?
%% For example X=2
% \psset{linestyle=dashed,linecolor=red,linewidth=0.5}
% \psline(2,0)(2,\PsWhatValueY)
% \psline(0,\PsWhatValueY)(2,\PsWhatValueX)
%% For example Y=2
% \psline(0,2)(\PsWhatValueX,2)
% \psline(\PsWhatValueX,0)(\PsWhatValueX,2)
\end{pspicture}
\end{document}
--8<---------------cut here---------------end--------------->8---

Thankful for pointers,

Patrick
--
Ludwig Boltzmann, who spent much of his life studying statistical
mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on
the work, died similarly in 1933. Now it is our turn to study
statistical mechanics. Perhaps it will be wise to approach the subject
cautiously.  from "States of Matter" by David Goodstein