\documentclass[11pt]{amsart}
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{epstopdf}
\usepackage[top=15mm,bottom=18mm,left=30mm,right=20mm]{geometry}

\title{\Large{Linear Algebra}}
\begin{document}
\maketitle

..............
...............
......


\end{document}



Why the left margins are different between even pages and odd pages?

\setlength\oddsidemargin{}
\setlength\evensidemargin{}

that controls the margin in even and odd pages.

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