\documentclass{article}
\usepackage{amsthm,amssymb,amsmath} 
\usepackage{xepersian} 
\settextfont[Scale=1.1]{XB Niloofar}
\begin{document}
$\begin{array}{*{20}{c}}
{(a,c) \in \theta  \Rightarrow (ax,cx) \in \theta }\\
{(c,b) \in \Psi  \Rightarrow (cx,bx) \in \Psi }
\end{array} \Rightarrow (ax,bx) \in \theta .\Psi $
\end{document}