\documentclass{book}
\usepackage{graphicx}

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{mathtools}
\usepackage{mathabx}
\usepackage{xepersian}

\begin{document}
${\upaccent{\aboxsplit{.}}}{x}_{1}=x_{2}$

  

\end{document}