\documentclass{article}
\usepackage{amsmath}
\usepackage{xepersian}
\begin{document}
\begin{equation}
\begin{aligned}
\lambda_k(A)&= \max\limits_{S_k}\min\limits_{x\in S_k, \|x\|=1} \langle Ax,x\rangle \\
\lambda_k(A)&= \min\limits_{S_{k-1}}\max\limits_{x\in S_{k-1}^{\perp}, \|x\|=1} \langle Ax,x\rangle
\end{aligned}
\end{equation}
\end{document}