\begin{pspicture}(-0,-5)(8,2)
  \psaxes
  [
		%ytrigLabels=true,
        linewidth=\pslinewidth,
        %labelFontSize=\scriptscriptstyle,
        tickcolor=gray,
        ticksize=-1.5pt 1.5pt,
        xlabelsep=0pt,
        arrowscale=2, % Taille des flèches
        %trigLabelBase=4,
        %Dx=5, % On ajoute 5
        %dx=1, % tous les 1 sur l'axe des abscisses
        %Dy=25,
        %dy=1,
]{->}(0,0)(-0.1,-5.1)(8,2)
  \psset{algebraic,linewidth=1.5pt}

  \savedata{\mydata}[{
      {2, -1}, {3, -1.5}, {4, -2}, {7, -3.5}
  }]
\dataplot[linestyle=dashed,plotstyle=curve,showpoints,linecolor=black!50]{\mydata}

\end{pspicture}