\begin{pspicture}(-3,-1)(3,6)
\psset{xunit=1 cm,algebraic=true}
\def\f{x*x+1}
\def\g{1/(\f)}
\psaxes{->}(0,0)(-3,-1)(3,6)
\psplot[linecolor=red,linewidth=1.5pt]{-2.5}{2.5}{\f}
\psplot[linecolor=blue,linewidth=1.5pt]{-2.5}{2.5}{\g}
\end{pspicture}