\documentclass{minimal}
\usepackage{pstricks,pst-plot}
\usepackage{tikz}



\begin{document}



\begin{tikzpicture}[domain=0:4]
    \draw[very thin,color=gray] (-0.1,-1.1) grid (3.9,3.9);
    \draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$};
    \draw[->] (0,-1.2) -- (0,4.2) node[above] {$f(x)$};
    \draw[color=red] plot[id=x] function{x} 
        node[right] {$f(x) =x$};
    \draw[color=blue] plot[id=sin] function{sin(x)} 
        node[right] {$f(x) = \sin x$};
    \draw[color=orange] plot[id=exp] function{0.05*exp(x)} 
        node[right] {$f(x) = \frac{1}{20} \mathrm e^x$};
\end{tikzpicture}

\vfill
\begin{pspicture}(-2,-2)(2,2)
\psaxes{->}(0,0)(-2,-2)(2,2)
\end{pspicture}
\end{document}