alignline-breakingmath-modemultline
I have long equation $F=\left\{ abcdef \right\}$ which needed to break line at halfway. To do it I use \begin{multline}.
\begin{multline}
F = \left\{ abc \right.\nonumber\\
\left. {} + def \right\},
\end{multline}
I also need to break curly bracket over the multiple lines, which I do with \right.\nonumber\\.
q1) How to align the equals sign of top line with + sign of bottom line in this case?
q2) How to display equation number?
Use either breqn to break lines automatically or use amsmath and its many environments exactly for this purpose. For example, with breqn:
\documentclass{article}
\usepackage{breqn}
\begin{document}
\begin{dmath}
Q(\lambda,\hat{\lambda}) = -\frac{1}{2} P{(O \mid \lambda )} \sum_s \sum_m \sum_t \gamma_m^{(s)} (t) \left( n \log(2 \pi ) + \log \left| C_m^{(s)} \right| + \left( \mathbf{o}_t - \hat{\mu}_m^{(s)} \right) ^T C_m^{(s)-1} \left(\mathbf{o}_t - \hat{\mu}_m^{(s)}\right) \right)
\end{dmath}
\end{document}
Note, the expression around \mid required braces to prevent it from breaking at this point; I'm sure there is a better way to do that; anyway, here's the output:
With amsmath, you need to specify the break points manually: (as others have also mentioned)
\usepackage{amsmath}
...
\begin{multline}
A+B+C+ \\ +D+E+F
\end{multline}
The users guide to amsmath is called amsldoc.pdf, but you can access it by typing texdoc amsmath on the command line. The main environments you'll use there would be align, split, and multline.
I'd much prefer Jubobs's approach, but just to show another method, you can split into two lines the radicand:
\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{fourier}
\usepackage[left=3cm,right=3cm,top=2.5cm,bottom=2cm]{geometry}
\begin{document}
\[
V_{DABC}=\dfrac{1}{6}\cdot DA \cdot DB \cdot DC \cdot
\sqrt{
\begin{aligned}
1+&2\cos\widehat{ADB}\cos\widehat{BDC}\cos\widehat{ADC} \\
& -\cos^2 \widehat{ADB} -\cos^2 \widehat{ADC} -\cos^2 \widehat{BDC}
\end{aligned}
}
=\dfrac{2\sqrt{2}}{3}.
\]
\end{document}
I removed the unnecessary centered dots.
Best Answer
First option does what you want, although I prefer second solution with
+not aligned with=.