LaTeX lists multiple formulas

1. gatherUsage

Basic usage, formula number

\begin{gather}
a+b = b+a \\
a\times b = b \times a
\end{gather}

$$\begin{array}{c}a+b=b+a\\ a\times b=b\times a\end{array}$$
gather*No number can be used

\begin{gather*}
a+b = b+a \\
a\times b = b \times a
\end{gather*}

$$\begin{array}{c}a+b=b+a\\ a\times b=b\times a\end{array}$$
Or use the command \\before \notagto prevent the specified line from being numbered,
$$\begin{array}{c}a+b=b+a\\ a\times b=b\times a\\ a-b=-b+a\end{array}$$

2. alignEnvironment

gatherEach line of formula in the environment is in-play, and aligncan be aligned according to the equal sign or other relational symbols

\begin{align}
a+b &= b+a \\
a\times b  + 1 &= b \times a + 1
\end{align}

$$\begin{array}{rl}a+b& =b+a\\ a\times b+1& =b\times a+1\end{array}$$

3. alignatEnvironment

alignatThe environment increases the spacing manually, and there is a parameter that indicates the number of formulas to be aligned in each row, in groups of two columns. For example, set the column spacing to one, which is \quad1em.

\begin{alignat}{2}
x &= \sin t & \quad & \text{水平方向} \\
y &= \cos t && \text{垂直方向}
\end{alignat}

$$\begin{array}{rlrl}x& =\sin t& & \text{horizontal direction}\\ y& =\cos t& & \end{array}$$

4. casesEnvironment

Enclose several lines of formulas in curly braces

\begin{equation}
f(x) = \begin{cases}
1, & \text{if } x \in [0, 1]; \\
0, & \text{if } x \in [-1, 0).
\end{cases}
\end{equation}

$$\begin{array}{c}f(x)=\{\begin{array}{ll}1,& \text{if }x\in [0,1];\\ 0,& \text{if }x\in [-1,0).\end{array}\end{array}$$