单行
$$ f(x)=x $$
$$
\sum_i^n +
\sum_{i=0}^{n}
$$
$$ x^2 + x_i $$
$$ \lbrace a+x \rbrace $$
$$
f(x)=\begin{cases}
1, & x>0\\
0, & x=0\\
-1, & x<0
\end{cases}
$$
$$ \langle x \rangle $$
$$ \lceil \frac{x}{2} \rceil $$
$$ \lfloor x \rfloor $
$$
\lbrace \sum_{i=0}^{n}i^{2}=\frac{2a}{x^2+1} \rbrace
$$
$$
\left\lbrace
\sum_{i=0}^{n}i^{2}=\frac{2a}{x^2+1}
\right\rbrace
$$
$$ \int_{1}^{\infty} $$
$$
\prod_{1}^{n} +
\bigcup_{1}^{n} +
\iint_{1}^{n}
$$
$$
\frac ab + \frac{1}{2} + {a+1 \over b+1}
$$
$$
\sqrt[x+1 ]{(x+1)^2}
$$
$$ \lim_{x\to +\infty} $$
$$ x_n\stackrel{p}\longrightarrow0 $$
$$ \vec{a} + \overrightarrow{a} $$
$$ \hat y=a\hat x+b $$
$$ \mathtt{X}' $$
$$
\begin{matrix}
1 & 2 & 3 \\
4 & 5 & 6 \\
7 & 8 & 9
\end{matrix} \tag{1}
$$
$$
\left\{
\begin{matrix}
1 & 2 & 3 \\
4 & 5 & 6 \\
7 & 8 & 9
\end{matrix}
\right\} \tag{2}
$$
$$
\left[
\begin{matrix}
1 & 2 & 3 \\
4 & 5 & 6 \\
7 & 8 & 9
\end{matrix}
\right] \tag{3}
$$
$$
\left[
\begin{matrix}
1 & 2 & \cdots & 4 \\
7 & 6 & \cdots & 5 \\
\vdots & \vdots & \ddots & \vdots \\
8 & 9 & \cdots & 0 \\
\end{matrix}
\right] \tag{4}
$$
$$
\left[
\begin{array}{cc|c}
1 & 2 & 3 \\
4 & 5 & 6
\end{array}
\right] \tag{5}
$$
$$
\begin{aligned}
a &= b + c\\
&= d + e + f
\end{aligned}
$$
$$
\prod_{{
\begin{gathered}
1\le i \le n\\
1\le j \le m
\end{gathered}
}}
M_{i,j}
$$
$$
\begin{aligned}
\boxed{x^2+y^2 = z^2}
\end{aligned}
$$
$$
z = \overbrace{
\underbrace{x}_\text{real} + i
\underbrace{y}_\text{imaginary}
}^\text{complex number}
$$
$$
\sum \\
\div \\
\cdot \\
\ast \\
\bigotimes \\
\bigoplus \\
\cdots \\
\lambda \\
\mu \\
\theta \\
\pi \\
\notin \\
\times
$$