[Tex/LaTex] breqn package is not working

Question

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}

Answer 1

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}
\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}