\documentclass{article}
\usepackage{tikz}
\usepackage{xepersian}
\settextfont{XB Niloofar}
\setdigitfont[Scale=1.1]{XB Zar}
\begin{document}
\begin{tikzpicture}[domain=-4:4]
\draw[->] (-3,0) -- (3,0);
\draw[->] (0,-3) -- (0,3);
\draw  plot  [domain=-2:2] (\x,2-\x^2)   node[right] {\scriptsize{$f= 2-x^{2} $}};
\draw plot [domain=-3:3] (\x,{cos(\x r)})   node[right] {\scriptsize{$g = \cos x$}};
 
\end{tikzpicture}
\end{document}