[pstricks] psplotTangent

[Denis Verges]

Hello,

%%%%%%%%%
\begin{center}
\psset{xunit=1cm,yunit=0.5cm}
\begin{pspicture*}(-3,-5)(6,6)
\psgrid[gridlabels=0pt,subgriddiv=1,gridwidth=0.1pt]
\psaxes[linewidth=1.25pt,Dx=10,Dy=10](0,0)(-3,-5)(6,6)
\psaxes[linewidth=1.5pt]{->}(0,0)(1,1)
\psplot[plotpoints=2000,linewidth=1.25pt,linecolor=red]{-2}{5}{x dup mul 3 mul 5 x mul sub 1 add}
\psplotTangent[linecolor=blue]{0}{10}{x dup mul 3 mul 5 x mul sub 1 add}
\psplotTangent[linecolor=blue]{2}{10}{x dup mul 3 mul 5 x mul sub 1 add}
\uput[ur](0,1){A}\uput[r](2,3){B} \uput[l](1,-4){C}\uput[r](-0.7,5.5){\red $\mathcal{P}$}
\end{pspicture*}
\end{center}
%%%%%%%%%
Why the tangent in x = 0 is false ?
Thanks.
Denis
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