[pstricks] How to show a specific point of a function's curve?

[Denis Bitouzé]

Hello,

let say we have a curve of a function:

\documentclass{article}
\usepackage{pst-plot}
\usepackage{pstricks-add}
\psset{algebraic=true}
\begin{document}
\begin{psgraph}(0,0)(5,3){6cm}{!}
  \psplot{0}{5}{x^2/10}
\end{psgraph}
\end{document}

What would be the best way to show the point of the curve (with a qdisk
on the point and two parallel lines for its x- and y-values) just by
specifying its x-value?

Thanks in anticipation.
-- 
Denis