# Problem with splitting a long fractional equation

I have a long equation

$$\Theta_{K} (\Delta t, \omega_{L}) = \frac{A}{2} \left[\frac{exp(-\Delta t/T_{2}^{*})\left[exp(- i \omega_{L} \Delta t)\left(exp(t_{rep}/T_{2}^{*} - i \omega_{L} t_{rep} - 1)\right) + exp(i \omega_{L} \Delta t) \left(exp(t_{rep}/T_{2}^{*} + i \omega_{L} t_{rep} - 1)\right) \right]}{exp\left(2 t_{rep}/T_{2}^{*}\right) + 1 - 2Re \left(exp(t_{rep}/T_{2}^{*} + i \omega_{L} t_{rep} - 1)\right)}\right]$$


which does not fit on single line. How can I split this over two lines?

• There are different solutions, try tex.stackexchange.com/questions/3782 for example. Commented Jan 14, 2017 at 22:27
• @Salim Bou I tried \begin{multline} \Theta_{K} (\Delta t, \omega_{L}) = \frac{A}{2} \left[\frac{exp(-\Delta t/T_{2}^{})\left[exp(- i \omega_{L} \Delta t)\left(exp(t_{rep}/T_{2}^{} - i \omega_{L} t_{rep} - 1)\right)}{exp\left(2 t_{rep}/T_{2}^{}\right) + 1 - 2Re \left(exp(t_{rep}/T_{2}^{} + i \omega_{L} t_{rep} - 1)\right)} \right] \\ + \left[\frac{exp(i \omega_{L} \Delta t) \left(exp(t_{rep}/T_{2}^{} + i \omega_{L} t_{rep} - 1)\right)}{exp\left(2 t_{rep}/T_{2}^{}\right) + 1 - 2Re \left(exp(t_{rep}/T_{2}^{*} + i \omega_{L} t_{rep} - 1)\right)}\right] \end{multline} but didn't work for me Commented Jan 14, 2017 at 23:13

You can factor out common sub-expressions.

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator\RE{Re}
\newcommand\trep{t_{\mathrm{rep}}}
\begin{document}
\begin{align}
\hspace{-1em}
\Theta_{K} (\Delta t, \omega_{L})
&= \frac{A}{2}
\left[\frac{\exp(-\Delta t/T_{2}^{*})\left[\Phi(-1)+\Phi(+1)\right]}%
{\exp\left(2 \trep/T_{2}^{*}\right) + 1 - 2\RE \left(\exp(\trep/T_{2}^{*}
+ i \omega_{L} \trep - 1)\right)}\right]\\
\intertext{where}
\Phi(\sigma) &=
\exp(\sigma\omega_{L} \Delta t)\exp(\trep/T_{2}^{*} +\sigma i \omega_{L} \trep - 1)\notag
\end{align}
\end{document}