Unable to split a long equation

Question

I want this equation to break into different lines at each of the line breaks indicated below.

f = c_{A1}x_{A1}+c_{A2}x_{A2}+c_{A3}x_{A3}+c_{B1}x_{B1}+c_{B2}x_{B2}+c_{B3}x_{B3} \\ 
+ c_{X1}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X1} \\
+ c_{X2}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X2} \\ 
+ c_{X3}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X3}

The line breaks are not working. I tried using the \usepackage{amsmath} option and the \begin{align} option with & to align the split equatio but it just returns an error when I compile the whole document.

Is there anyway around this problem?

Answer 1

It should work.

Here are two ideas to split one equation on more lines. (The align family is used to align more than one equation.)

Code

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{multline}
f  = c_{A1}x_{A1}+c_{A2}x_{A2}+c_{A3}x_{A3}+c_{B1}x_{B1}+c_{B2}x_{B2}+c_{B3}x_{B3} \\ 
    + c_{X1}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X1} \\
    + c_{X2}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X2} \\ 
    + c_{X3}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X3}
\end{multline}

\begin{equation}
\begin{split}
f &  = c_{A1}x_{A1}+c_{A2}x_{A2}+c_{A3}x_{A3}+c_{B1}x_{B1}+c_{B2}x_{B2}+c_{B3}x_{B3} \\ 
 & \hphantom{{}={}}  + c_{X1}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X1} \\
 & \hphantom{{}={}}   + c_{X2}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X2} \\ 
 & \hphantom{{}={}}   + c_{X3}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X3}
\end{split}
\end{equation}
\end{document}

Output

Answer 2

For example:

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\[
\begin{split}
        f &= c_{A1}x_{A1}+c_{A2}x_{A2}+c_{A3}x_{A3}+c_{B1}x_{B1}+c_{B2}x_{B2}+c_{B3}x_{B3} \\ 
  & \quad{} + c_{X1}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X1} \\
   & \quad{}+ c_{X2}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X2} \\ 
  & \quad {}+ c_{X3}[y_X,(W/S)_X,(T/W)_X,(AR)_X]X_{X3}
\end{split}
\]

\end{document}