# introduce a line break in a long equation

\documentclass[12pt,twoside,a4paper,openright]{report}
\usepackage[portuguese]{babel}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\usepackage{amsmath}

\begin{document}
$$\label{equacao_silica} \binom{\text{Quantidade}}{\text{Sílica (\% (w/w))}} = 100 - \left[\binom{\text{Perda de Massa}}{\text{(580\degree C-900\degree C)} \times \frac{100,1}{44}} - \binom{\text{Perda de Massa}}{\text{(30\degree C-200\degree C)}} - \binom{\text{\% Resíduos}}{\text{GCC}} \right]\\$$

\end{document}


How I can introduce a line break in this equation ?

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For example (the presence of - at the end of line depends on typographic rules in your country):

\documentclass[12pt,twoside,a4paper,openright]{report}
\usepackage[portuguese]{babel}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\usepackage{amsmath}

\begin{document}
\label{equacao_silica} \begin{aligned} &\binom{\text{Quantidade}}{\text{Sílica (\% (w/w))}} = 100 - {}\\ &\qquad{} - \left[\binom{\text{Perda de Massa}}{\text{(580\degree C-900\degree C)} \times \frac{100,1}{44}} - \binom{\text{Perda de Massa}}{\text{(30\degree C-200\degree C)}} - \binom{\text{\% Resíduos}}{\text{GCC}} \right]\\ \end{aligned}

\end{document}


Probably some other environment, e.g. gathered, may be more suitable; aligned is only an example.

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I have a problem with this code –  user46548 Jul 17 '14 at 17:56
@user46548 What a problem? –  Przemysław Scherwentke Jul 17 '14 at 17:57
command \ohm already defined –  user46548 Jul 17 '14 at 18:01
@user46548 You have \degree in your code, hence I have assumed that the package siunits is missing. If not, comment that line and use your definition of \degree. There is no \ohm in your example. –  Przemysław Scherwentke Jul 17 '14 at 18:12

There are many possibilities for introducing a line break. A key step is not to use \left and \right to size the square brackets, since you can't have a line break across a \left-\right pair.

Here are two possible solutions, one using the multline environment, the other the split environment nested inside an equation environment.

\documentclass[12pt,twoside,a4paper,openright]{report}
\usepackage[portuguese]{babel}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
%\usepackage{amsmath}  % is loaded automatically by 'mathtools'
\newcommand\degree{\ensuremath{^{\circ}}} %% correct this if necessary

\begin{document}
\begin{multline}
\label{equacao_silica}
= 100 - \biggl\{\binom{\text{Perda de Massa}}{\text{(580\degree C--900\degree C)}
\times \frac{100,1}{44}} \\
- \binom{\text{Perda de Massa}}{\text{(30\degree C--200\degree C)}}
-  \binom{\text{\% Resíduos}}{\text{GCC}} \biggr\}
\end{multline}

$$\begin{split} \label{equacao_silica} \binom{\text{Quantidade}}{\text{Sílica (\% (w/w))}} &= 100 - \biggl\{\binom{\text{Perda de Massa}}{\text{(580\degree C--900\degree C)} \times \frac{100,1}{44}} \\ &\quad{}- \binom{\text{Perda de Massa}}{\text{(30\degree C--200\degree C)}} - \binom{\text{\% Resíduos}}{\text{GCC}} \biggr\} \end{split}$$

\end{document}


By the way, I think en-dashes (--) instead of single dashes should be used to indicate the temperature ranges.

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