Equation:
\begin{equation}
E = mc^2
\end{equation}
Equation*:
\begin{equation*}
E = mc^2
\end{equation*}
Brackets:
E = mc^2
Brackets tagged:
E = mc^2\tag{x}
Split:
\begin{equation}
\begin{split}
a& =b+c-d\\
& \quad +e-f\\
& =g+h\\
& =i
\end{split}
\end{equation}
Multline:
\begin{multline}
a+b+c+d+e+f+g\\
M+N+O+P+Q\\
R+S+T\\
u+v+w+x+y+z
\end{multline}
Multline*:
\begin{multline*}
a+b+c+d+e+f+g\\
M+N+O+P+Q\\
R+S+T\\
u+v+w+x+y+z
\end{multline*}
Gather:
\begin{gather}
a_1=b_1+c_1\\
a_2=b_2+c_2-d_2+e_2
\end{gather}
Gather*:
\begin{gather*}
a_1=b_1+c_1\\
a_2=b_2+c_2-d_2+e_2
\end{gather*}
Align:
\begin{align}
a_1& =b_1+c_1\\
a_2& =b_2+c_2-d_2+e_2
\end{align}
Align*:
\begin{align*}
a_1& =b_1+c_1\\
a_2& =b_2+c_2-d_2+e_2
\end{align*}
Align:
\begin{align}
a_{11}& =b_{11}& a_{12}& =b_{12}\\
a_{21}& =b_{21}& a_{22}& =b_{22}+c_{22}
\end{align}
Align with \notag and \tag:
\begin{align}
a_{11}& =b_{11}& a_{12}& =b_{12}\notag\\
a_{21}& =b_{21}& a_{22}& =b_{22}+c_{22} \tag{y}
\end{align}
Align* with \tag:
\begin{align*}
a_1& =b_1+c_1\tag{z}\\
a_2& =b_2+c_2-d_2+e_2
\end{align*}