如何通过三点C2',Q',C1'画一条抛物线？

Question

\documentclass[border=15pt,pstricks,12pt]{standalone}
\usepackage{pst-eucl,pstricks-add,pst-intersect}
\begin{document}
\begin{pspicture}[showgrid](-7,-2)(6,6)
\pnodes(-1,2){M}(4,-.5){N}(-1,-1){X}(0,5){Y}(2,-1){Q}
\psline(X)(Y)
\pssavepath{parabol}{\parabola(4,3)(Q)}
\pssavepath{lineMN}{\psline(M)(N)}
\psintersect[name=C,showpoints]{parabol}{lineMN}
\pstOrtSym{X}{Y}{C1,C2,Q}
\parabola(C1')(Q')
\end{pspicture}
\end{document}

Answer 1

你正在寻找一个镜像抛物线：

\documentclass{article}
\usepackage{pst-eucl,pst-intersect,pst-optic,pstricks-add}
\begin{document}

\begin{pspicture}[showgrid](-7,-2)(6,6)
    \pnodes(-1,2){M}(4,-.5){N}(-1,-1){X}(0,5){Y}(2,-1){Q}
    \psline(X)(Y)
    \pssavepath{parabol}{\parabola(4,3)(Q)}
    \pssavepath{lineMN}{\psline(M)(N)}
    \psintersect[name=C,showpoints]{parabol}{lineMN}
    \pstOrtSym{X}{Y}{C1,C2,Q}
    \parabola(C1')(Q')
  \psset{linewidth=1.5pt}   
  \parabola[linecolor=red](4,3)(Q)% same as (x-2)^2-1
  \symPlan(X)(Y){\psplot[linecolor=blue,algebraic]{0}{4}{(x-2)^2-1}}
\end{pspicture}

\end{document}