\documentclass{article}
\usepackage{pgfplots}
\usepackage{xepersian}
\settextfont{Yas}
\setdigitfont{Yas}
\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 (\x,\x) node[right] {$f(x) =x^2$};
% \x r means to convert ’\x’ from degrees to _r_adians:
\draw[color=blue] plot (\x,{sin(\x r)}) node[right] {$f(x) = \sin x$};
\draw[color=orange] plot (\x,{0.05*exp(\x)}) node[right] {$f(x) = \frac{1}{20} \mathrm e^x$};
\end{tikzpicture} 
               

\begin{tikzpicture}
\begin{axis}
    \addplot[
        red, domain=0:100,
        samples=10,
    ]
    {500*(exp x)};
\end{axis}    
\end{tikzpicture}

\end{document}