\documentclass[12pt]{report}
\usepackage{amsthm,amssymb,amsmath}
\usepackage{xepersian}
\settextfont[Scale=1.2]{XB Niloofar}
%\setromantextfont[Scale=1]{Junicode}
\setdigitfont[Scale=1.0]{XB Niloofar}
\usepackage{tocbibind}
\usepackage[top=40mm, bottom=15mm, left=12mm, right=12mm]{geometry}
\renewcommand{\baselinestretch}{1.2}
\begin{document}
\begin{itemize}

\item
\vspace{1cm}

\centerline{**************}
\item
\vspace{1cm}

\centerline{**************}



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 %\begin{figure} 

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\item  
 همگرایی یا واگرایی سریها و انتگرالهای مجازی زیر را تعیین کنید.
 (فقط به 2 مورد پاسخ دهید هر کدام 1 نمره)
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 \centerline{
 $(a)\displaystyle\sum\displaystyle\frac{\sqrt[3]{n^3+2}}{n^2+4n+7}~~~~~~~~~~~~~~(b)\displaystyle\sum\displaystyle\frac{n!(2n)!}{(3n)!}~~~~~~~~~~~~(c)\displaystyle\int_e^{\infty}\displaystyle\frac{dx}{x(lnx)^2}$}

\end{itemize}
\vspace{3cm}

\centerline{موفق باشید                                                                                                                                                                                                                                        }
 \end{document}