\documentclass{article}
\usepackage{pgfkeys,diagbox,tikz}
\usepackage{mathabx}
\usepackage{xepersian}
\settextfont{Yas}
\setdigitfont{Yas}
\begin{document}
\usetikzlibrary{positioning,decorations.pathreplacing,matrix}
\usetikzlibrary{mindmap,trees,shadows}
\usetikzlibrary{patterns}
 \tikzstyle{state}=[thick,scale=1] 
 \begin{tikzpicture}
\draw[->] (0,0) -- (5.5,0) node[right] {$X$};
\draw[->] (0,0) -- (0,5.5) node[above] {$Y$};
         \draw (0,1pt) -- (0,-1pt) node[below] {$0$};
        \draw (2,1pt) -- (2,-1pt) node[below] {};
        \draw (0pt,2) -- (-2pt,2) node[left] {};
        \draw (0pt,3) -- (-2pt,3) node[left] {};
  \draw[style = dashed] (2,0) -- (2,2);
  \draw[style = dashed] (0,2) -- (2,2);
   \draw[style = dashed] (3,0) -- (3,3);
    \draw[style = dashed] (0,3) -- (3,3);
   \draw[style=smooth]plot coordinates{(1.6,1.2)(1.8,1.55)(1.9,1.8)(2,2)(2.35,2.65)(3,3)(4.1,3.1)(5,4)};
   \node [state](A)[yshift=5cm,xshift=4cm] {$y=f(x)$};
    \node [state](B)[yshift=-1cm,xshift=2cm] {$\text{ب}$};
    \node [state](C)[draw=none,scale=0.68,yshift=-0.8cm,xshift=3.7cm] {${\LARGE \underbrace{}_{A}}$};
     \node [state](D)[yshift=2.7cm,xshift=-1.2cm,scale=0.95] {$B=f(A) \lbrace $};
\end{tikzpicture}
\end{document}