\begin{align}
\begin{cases}
a_2=b_2+1 \\ x=2 y^2
\end{cases}
\end{align}
\frac{-b\pm\sqrt{b^2-4\acute{a}c}}{2\acute{a}}
f(n) =
\begin{cases}
n/2, & \mbox{if }n\mbox{ is even} \\
3n+1, & \mbox{if }n\mbox{ is odd}
\end{cases}
\begin{align}
f(x) & = (m+n)^2 \\
& = m^2+2mn+n^2 \\
\end{align}
\begin{alignat}{2}
f(x) & = (m-n)^2 \\
f(x) & = (-m+n)^2 \\
& = m^2-2mn+n^2 \\
\end{alignat}
多行等式（左对齐）
\begin{array}{lcl}
z & = & a \\
f(x,y,z) & = & x + y + z
\end{array}
\begin{array}{lcl}
z & = & a \\
f(x,y,z) & = & x + y + z
\end{array}
多行等式（右对齐）
\begin{array}{lcr}
z & = & a \\
f(x,y,z) & = & x + y + z
\end{array}
长公式换行
\begin{split}
x &= \sqrt {1-y^2}\\
x &= \sqrt[3]{1-y^3}
\end{split}
\begin{align}
x &= \sqrt {1-y^2}\\
x &= \sqrt[3]{1-y^3}
\end{align}
方程组
\begin{cases}
3x + 5y + z \\
7x - 2y + 4z \\
-6x + 3y + 2z
\end{cases}
\begin{cases}
3x + 5y + z \\
7x - 2y + 4z \\
-6x + 3y + 2z
\end{cases}
\begin{cases}
3x + 5y + z \\
7x - 2y + 4z \\
-6x + 3y + 2z
\end{cases}
