% F(t)=-1+2t
   \newlpoly{\poliF}{-1}{2}
% G(t)=-1+2t+t^2
   \newqpoly{\poliG}{-1}{2}{1}
% H(t)=-1+2t+t^2-0,5t^3
   \newcpoly{\poliH}{-1}{2}{1}{-0.5}

\setlength{\unitlength}{1cm}
\begin{Picture}(-4.5,-5.5)(4.5,5.5)
\cartesianaxes(-4,-5)(4,5)
\pictcolor{blue}
\PlotFunction{\poliF}{-2}{3}
\pictcolor{red}
\PlotFunction{\poliG}{-3.5}{1.5}
\pictcolor{orange}
\PlotFunction[10]{\poliH}{-2}{3.5}
\end{Picture}
