\begin{pspicture}(-5,-5)(5.2,5.2)
  \psgrid[griddots=10,gridlabels=0pt, subgriddiv=0, gridcolor=black!40]
  \psaxes
  [
		%ytrigLabels=true,
        linewidth=\pslinewidth,
        %labelFontSize=\scriptscriptstyle,
        tickcolor=gray,
        ticksize=-1.5pt 1.5pt,
        xlabelsep=3pt,
        arrowscale=1,
        %trigLabelBase=4,
]{->}(0,0)(-5,-5)(5,5)[$x$,90][$f(x)$,0]
  \psset{algebraic,linewidth=1.5pt}

  \psplot[linecolor=red]{-5}{5}{-2*x}
  \psplot[linecolor=blue]{-5}{5}{-1.5*x}
\end{pspicture}