% 导言区 进行全局设置
\documentclass{article}%book, report, letter
\title{My First Document}
\author{Ding}
\date{\today}
% 正文区(文稿区)
\begin{document}
\maketitle
Hello World!
% here is my big formula
%一个$行内公式,两个$行间公式
Let $f(x)$ be define by the formula
$$f(x)=3x^2+x-1$$ which is a polynomial of degree 2.
\end{document}