\documentclass{imsproc}
\usepackage[extrafootnotefeatures]{xepersian}
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\begin{document}
\begin{eqnarray*} 
E[Z]&=&\mu + \sqrt{\frac{2}{\pi}}\frac{\lambda}{\sqrt{1+\lambda^2}}\sigma\\ 
var[Z]&=&(1-\frac{2\lambda^2}{\pi(1+\lambda^2)})\sigma^2\\ 
\gamma &=&\frac{1}{2}(4-\pi)(\frac{E^2[X]}{\var[\frac{(Z-\mu)}{\sigma}]})^{3/2}\\ 
K &=& 2(\pi-3)(\frac{E^2[\frac{(Z-\mu)}{\sigma}]}{\var[\frac{(Z-\mu)}{\sigma}]})^2\\ 
\end{eqnarray*}
\end{document}