# Split equation problem

I would like to split the following equation in two parts. Very basic thing, seems to be.

\begin{equation}
\zeta_k(x) = \frac{\sin (\frac{1}{2} (x - x_0)) \cdots \sin(\frac{1}{2} (x-x_{k-1}))}
{ \sin ( \frac{1}{2} (x_k - x_0)) \cdots \sin(\frac{1}{2} (x_k - x_{k-1}))} %
%
\frac{\sin ( \frac{1}{2} (x - x_{k+1})) \cdots %
\sin(\frac{1}{2} (x - x_{2n}))}{\sin(\frac{1}{2} (x_k - x_{k+1})) \cdots %
\sin(\frac{1}{2} (x_k - x_{2n}))}
\label{eq3}
\end{equation}


I inserted amsmath package and tried with begin split and so on but can not get to the point where I separate the equation into two lines, one that contains

\zeta_k(x) = \frac{\sin (\frac{1}{2} (x - x_0)) \cdots \sin(\frac{1}{2} (x-x_{k-1}))}
{ \sin ( \frac{1}{2} (x_k - x_0)) \cdots \sin(\frac{1}{2} (x_k - x_{k-1}))} %
%


and the other that contains

\frac{\sin ( \frac{1}{2} (x - x_{k+1})) \cdots %
\sin(\frac{1}{2} (x - x_{2n}))}{\sin(\frac{1}{2} (x_k - x_{k+1})) \cdots %
\sin(\frac{1}{2} (x_k - x_{2n}))}


any suggestions?

• What error messages are you seeing? When I put \begin{split} ... \\ ... \end{split} in the right places then I get a decent output. Can you post the exact code that you tried that didn't work? – Loop Space Mar 31 '11 at 11:12
• (For "the right places", see daleif's answer.) – Loop Space Mar 31 '11 at 11:15
• Just a minor suggestion: to improve readability I would use \sin\bigl(\frac{1}{2} (x - x_0)\bigr) instead of \sin(\frac{1}{2} (x - x_0)) (similar remark applies to all the other factors). – Gonzalo Medina Mar 31 '11 at 17:29
• I realized that the problem has to do with my mac tex installation, since compilation in linux finally worked – Open the way Apr 1 '11 at 8:22
• @gnu_drug amsmath is very stable; I don't think it could be MacTeX that was the problem... – Will Robertson Apr 1 '11 at 13:00

## 1 Answer

I'd use (memoir not relevant)

\documentclass[a4paper]{memoir}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{split}
\zeta_k(x) ={} & \frac{\sin (\frac{1}{2} (x - x_0)) \cdots
\sin(\frac{1}{2} (x-x_{k-1}))} { \sin ( \frac{1}{2} (x_k - x_0))
\cdots \sin(\frac{1}{2} (x_k - x_{k-1}))} %
%
\\
& \times \frac{\sin ( \frac{1}{2} (x - x_{k+1})) \cdots %
\sin(\frac{1}{2} (x - x_{2n}))}{\sin(\frac{1}{2} (x_k -
x_{k+1})) \cdots %
\sin(\frac{1}{2} (x_k - x_{2n}))}
\end{split}
\label{eq3}
\end{equation}
\end{document}