\documentclass[12pt]{report}
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\usepackage{mathtools,amssymb}
\usepackage{amsthm,amssymb}
\usepackage{amsmath}
\usepackage{titletoc}
\usepackage{fancyhdr}
\usepackage{graphicx}
\usepackage{amsfonts}
\usepackage{float}
\usepackage{caption}
\newcommand{\cchapter}[1]{\chapter[#1]{\centering #1}}
\baselineskip=.75cm
\usepackage[computeautoilg=off,extrafootnotefeatures]{xepersian}
\defpersianfont\myFafont[Scale=1]{IRNazanin}
\settextfont[Scale=1]{B Nazanin}
 \setlatintextfont[Scale=0.9]{Times New Roman}
\theoremstyle{definition}
\newtheorem{theorem}{قضیه}[chapter]
\begin{document}
\begin{theorem}
$x=0$
نقطه‌ تعادل سیستم غیرخطی مرتبه‌ی کسری   
\end{theorem}
 %%%%%%%%%%%%%%%%%%%%%
\end{document}