\documentclass{article}
\usepackage{amsmath}
\usepackage{xepersian}
\settextfont{XB Zar}
\setlatintextfont{Linux Libertine}
\setdigitfont{XB Zar}
\begin{document}
\begin{center}
\fbox{
\begin{minipage}{0.5\textwidth}
\begin{align*}
(x-y)&=x+y\\
(x-y)&=x+y\\
(x-y)&=x+y\\
(x-y)&=x+y\\
(x-y)&=x+y\\
(x-y)&=x+y\\
(x-y)&=x+y\\
\end{align*}
\end{minipage}}
\end{center}
\end{document}