\documentclass[14pt]{book}
\usepackage[fleqn]{amsmath}
\usepackage{tikz}
\usetikzlibrary{positioning, decorations.pathmorphing}
\usepackage{xepersian}
\settextfont{B Nazanin}
\begin{document}
	\subsection
	{گشتاور عمومی(حول مبدا $a$)}
	\begin{equation*}
	M_r=\qquad\qquad
	\begin{array}{l c l}
	\text{داده‌های طبقه‌بندی نشده}&\longrightarrow&
	\frac{\sum\left(x_i-a\right)^r}{N}
	\\
	&&
	\\
	\text{داده‌های طبقه‌بندی شده}&\longrightarrow&
	\frac{\sum F_i\left(x_i-a\right)^r}{N} = 
	\sum f_i\left(x_i-a\right)^r
	\end{array}
	\end{equation*}
	\begin{tikzpicture}[overlay]%remember picture
	\draw[->,decorate, decoration=snake] (-10.4,1) -- (-9,1.25);
	\draw[->,decorate, decoration=snake] (-10.4,0.895) -- (-9,0.5);
	\end{tikzpicture}
\end{document}