# breqn package is not working

I am using the breqn package, but it is not working.

\begin{dmath}

\sqrt {-{\frac {-4\,c-k_{{2}}{x}^{2}+{x}^{2}\sqrt {4\,c+{k_{{2}}}^{2}}}{c}}}\sqrt {{\frac {4\,c+k_{{2}}{x}^{2}+{x}^{2}\sqrt {4\,c+{k_{{2}}}^{2}}}{c}}}{\it EllipticF} \left( 1/2\,x\sqrt {{\frac {-k_{{2}}+ \sqrt {
4\,c+{k_{{2}}}^{2}}}{c}}},1/2\,\sqrt {-{\frac {4\,c+2\,{k_{{2}}}^{2}+2\,k_{{2}}\sqrt {4\,c+{k_{{2}}}^{2}}}{c}}} \right) {\frac {1}{\sqrt {{\frac {-k_{{2}}+\sqrt {4\,c+{k_{{2}}}^{2}}}{c}}}}}{\frac {1}{\sqrt {8\,c-2\,{x}^{4}+4\,k_{{2}}{x}^{2}}}}=t
\end{dmath}

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Welcome to TeX.sx! Please add a minimal working example (MWE) that illustrates your problem. It is considered a lot better to put in some code that will compile, as it makes it a lot easier for us to copy it into our text editor and work with it, and see exactly what it is you are trying to do. –  Andrew Uzzell Nov 1 '12 at 10:25
Another tip: If you indent lines by 4 spaces, they'll be marked as a code sample. You can also highlight the code and click the "code" button (with "{}" on it). –  Andrew Uzzell Nov 1 '12 at 10:26

Examining your math expression, I can't see how it might be typeset across just two lines; at a minimum, three lines are required to typeset it properly. The following MWE does so, using the multline environment provided by the amsmath package.

\documentclass{article}
\usepackage{amsmath}
\begin{document}\pagestyle{empty}
\begin{multline*}
\sqrt {-\frac {-4c-k_2x^2+x^2\sqrt {4c+k_2^2}}{c}}\,
\sqrt {\frac {4c+k_2x^2+x^2\sqrt {4c+k_2^2}}{c}}\\
\times \textit{EllipticF}
\left( \frac{1}{2}x\sqrt {\frac {-k_2+ \sqrt {4c+k_2^2}}{c}},
\frac{1}{2}\sqrt {-\frac {4c+2k_2^2+2k_2\sqrt {4c+k_2^2}}{c}} \,\right) \\
\times \frac {1}{\sqrt \frac{-k_2+\sqrt {4c+k_2^2}}{c}}\,
\frac {1}{\sqrt {8c-2x^4+4k_2x^2}}=t
\end{multline*}
\end{document}


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To get the equation number (as in the original formula), use multline. I've come to a very similar input, removing the useless braces and many \, commands, adding the same as you did. :) However, I'm not very convinced about \times; perhaps \cdot? –  egreg Nov 1 '12 at 11:32
@egreg - \times may indeed be a bit too prominent, visually speaking. If so, \cdot would certainly be a plausible alternative. At any rate, it would seem to be a good idea to make explicit that the items across the three lines are being multiplied together, using any multiplication symbol that does the job. –  Mico Nov 1 '12 at 11:52

Taking @Mico's answer and removing the forced \\ breaks and going back to breqn you will see that breqn can break this although I couldn't see a way to get the indentation, so th emanual breaking is giving more pleasing appearance here, but sometimes manual breaking isn't really an option and breqn is what you want...

\documentclass{article}
\usepackage{breqn}
\begin{document}\pagestyle{empty}
\begin{dmath*}
\sqrt {-\frac {-4c-k_2x^2+x^2\sqrt {4c+k_2^2}}{c}}
\sqrt {\frac {4c+k_2x^2+x^2\sqrt {4c+k_2^2}}{c}}
\times \textit{EllipticF}
\left( \frac{1}{2}x\sqrt {\frac {-k_2+ \sqrt {4c+k_2^2}}{c}},
\frac{1}{2}\sqrt {-\frac {4c+2k_2^2+2k_2\sqrt {4c+k_2^2}}{c}} \,\right)
\times \frac {1}{\sqrt \frac{-k_2+\sqrt {4c+k_2^2}}{c}}
\frac {1}{\sqrt {8c-2x^4+4k_2x^2}}=t
\end{dmath*}
\end{document}

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