\documentclass[addpoints,12pt]{exam}
%\documentclass[a4paper]{article}
\usepackage{amsmath}
\usepackage{xepersian}
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\begin{document}
\begin{equation*}
\left\{
 \begin{array}{rl}
 \tilde{X}^\mu_{\alpha}=\left\{
\tilde{X}^{\mu L}_{2\alpha}\hspace{1.5cm}0<\alpha \leq 0.5\\
\tilde{X}^{\mu U}_{2(1-\alpha)}\qquad 0.5\leq \alpha\leq 1\\
\right.
\tilde{X}^{1-\nu}_{\alpha}=\left\{
 X^{{1-\nu}L}_{2\alpha}\qquad 0<\alpha \leq 0.5\\
 X^{{1-\nu}U}_{2(1-\alpha)}\qquad 0.5\leq\alpha\leq 1
\right.
  \end{array}
\end{equation*}
\end{document}