& =g+h\\ 
& =i 
\end{split} 
\end{equation} 

<hr>
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*}

<hr>
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*} 

<hr>
Align:

\begin{align} 
a_1& =b_1+c_1\\ 
a_2& =b_2+c_2-d_2+e_2 
\end{align}

Align*:

\begin{a