[Tex/LaTex] How to write a long equation in multi line scaled to text width

Question

I want to write a long equation over several lines, but result looks highly irregular.

How can write this equation better, preferably with all equation occupying the same wide?

\documentclass[12pt]{book}
\usepackage[]{breqn}‎

\usepackage{lipsum}‎
\begin{document}‎
How can I write equation beatifull. I want all equation the same of text width‎
\lipsum[1]
‎\begin{equation*}‎
‎\begin{split}‎
‎&+\left[ {{T}_{44}}\left( 1,2 \right) \right.+2{{T}_{44}}\left( 5,2 \right)+\left‎. ‎{{T}_{44}}\left( 2,2 \right) \right]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\eta }^{4}}}+\left[ {{T}_{44}}\left( 1,3 \right) \right.+2{{T}_{44}}\left( 5,3 \right)\\‎
‎&+\left‎. ‎{{T}_{44}}\left( 2,3 \right) \right]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{3}}\partial \eta }+\left[ {{T}_{44}}\left( 1,4 \right)+2{{T}_{44}}\left( 5,4 \right)+{{T}_{44}}\left( 2,4 \right) \right]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial \xi \partial {{\eta }^{3}}}\\‎
‎&+\left[ {{T}_{44}}\left( 1,5 \right)+2{{T}_{44}}\left( 5,5 \right)+{{T}_{44}}\left( 2,5 \right) \right]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{2}}\partial {{\eta }^{2}}}+\left[ {{T}_{43}}\left( 1,1 \right) \right.+2{{T}_{43}}\left( 5,1 \right)\\‎
‎&+\left‎. ‎{{T}_{43}}\left( 2,1 \right) \right]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\xi }^{3}}}+\left[ {{T}_{43}}\left( 1,2 \right)+2{{T}_{43}}\left( 5,2 \right)+{{T}_{43}}\left( 2,2 \right) \right]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\eta }^{3}}}\\‎
&+\left[ {{T}_{43}}\left( 1,3 \right)+2{{T}_{43}}\left( 5,3 \right)+{{T}_{43}}\left( 2,3 \right) \right]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\xi }^{2}}\partial \eta }++\left[ {{T}_{43}}\left( 1,4 \right) \right.+2{{T}_{43}}\left( 5,4 \right)\\‎
&+\left. ‎{{T}_{43}}\left( 2,4 \right) \right]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial \xi \partial {{\eta }^{2}}}+\left( {{T}_{42}}\left( 1,1 \right)+2{{T}_{42}}\left( 5,1 \right)+{{T}_{42}}\left( 2,1 \right) \right)\frac{{{\partial }^{2}}{{w}^{b}}}{\partial {{\xi }^{2}}}\\‎ 
&‎+\left[ {{T}_{42}}\left( 1,2 \right)+2{{T}_{42}}\left( 5,2 \right)+{{T}_{42}}\left( 2,2 \right) \right]\frac{{{\partial }^{2}}{{w}^{b}}}{\partial {{\eta }^{2}}}+\left[ {{T}_{42}}\left( 1,3 \right)‎+ ‎\right.2{{T}_{42}}\left( 5,3 \right)\\‎
&\left. +‎{{T}_{42}}\left( 2,3 \right) \right]\frac{{{\partial }^{2}}{{w}^{b}}}{\partial \xi \partial \eta }+\left[ {{T}_{41}}\left( 1,1 \right)+2{{T}_{41}}\left( 5,1 \right)+{{T}_{41}}\left( 2,1 \right) \right]\frac{\partial {{w}^{b}}}{\partial \xi }\\‎
&\left. +‎\left[ {{T}_{41}}\left( 1,1 \right)+2{{T}_{41}}\left( 5,1 \right)+{{T}_{41}}\left( 2,1 \right) \right]\frac{\partial {{w}^{b}}}{\partial \eta } \right\}-2\mu {{\tau }^{s}}\left\{ \left[ {{T}_{44}}\left( 1,1 \right)‎+ ‎\right.2{{T}_{44}}\left( 5,1 \right) \right.\\‎
&+\left. ‎{{T}_{44}}\left( 2,1 \right) \right]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{4}}}+\left[ {{T}_{44}}\left( 1,2 \right) \right.+2{{T}_{44}}\left( 5,2 \right)+\left‎. ‎{{T}_{44}}\left( 2,2 \right) \right]\frac{{{\partial }^{4}}{{w}^{s}}}{\partial {{\eta }^{4}}}+\left[ {{T}_{44}}\left( 1,3 \right) \right.‎‎
‎\end{split}‎‎‎
\end{equation*}‎

\end{document}

Here is an example output of the code above:

Answer 1

You have a lot of mis matched brackets ( and [ and { which makes the source and the output hard to follow. I assumed that they were intended to be matched and let Tex find the line breaks on its own:

\documentclass[12pt]{book}


\usepackage{lipsum}
\begin{document}‎
How can I write equation beatifull. I want all equation the same of text width‎
\lipsum[1]

‎\begin{center}
‎$\displaystyle
{[ {{T}_{44}}( 1,2 ) +2{{T}_{44}}( 5,2 )+‎{{T}_{44}}( 2,2 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\eta }^{4}}}}+
{[ {{T}_{44}}( 1,3 ) +2{{T}_{44}}( 5,3 )‎‎+‎{{T}_{44}}( 2,3 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{3}}\partial \eta }}+
{[ {{T}_{44}}( 1,4 )+2{{T}_{44}}( 5,4 )+{{T}_{44}}( 2,4 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial \xi \partial {{\eta }^{3}}}}‎+
{[ {{T}_{44}}( 1,5 )+2{{T}_{44}}( 5,5 )+{{T}_{44}}( 2,5 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{2}}\partial {{\eta }^{2}}}}+
{[ {{T}_{43}}( 1,1 ) +2{{T}_{43}}( 5,1 )‎+‎{{T}_{43}}( 2,1 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\xi }^{3}}}}+
{[ {{T}_{43}}( 1,2 )+2{{T}_{43}}( 5,2 )+{{T}_{43}}( 2,2 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\eta }^{3}}}}‎+
{[ {{T}_{43}}( 1,3 )+2{{T}_{43}}( 5,3 )+{{T}_{43}}( 2,3 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\xi }^{2}}\partial \eta }}+ 
{[ {{T}_{43}}( 1,4 ) +2{{T}_{43}}( 5,4 )‎+ ‎{{T}_{43}}( 2,4 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial \xi \partial {{\eta }^{2}}}}+
{[ {{T}_{42}}( 1,1 )+2{{T}_{42}}( 5,1 )+{{T}_{42}}( 2,1 ) )\frac{{{\partial }^{2}}{{w}^{b}}}{\partial {{\xi }^{2}}}}‎+
{[ {{T}_{42}}( 1,2 )+2{{T}_{42}}( 5,2 )+{{T}_{42}}( 2,2 ) ]\frac{{{\partial }^{2}}{{w}^{b}}}{\partial {{\eta }^{2}}}}+
{[ {{T}_{42}}( 1,3 )‎+ ‎2{{T}_{42}}( 5,3 )‎ +‎{{T}_{42}}( 2,3 ) ]\frac{{{\partial }^{2}}{{w}^{b}}}{\partial \xi \partial \eta }}+
{[ {{T}_{41}}( 1,1 )+2{{T}_{41}}( 5,1 )+{{T}_{41}}( 2,1 ) ]\frac{\partial {{w}^{b}}}{\partial \xi }}‎ +‎
{[ {{T}_{41}}( 1,1 )+2{{T}_{41}}( 5,1 )+{{T}_{41}}( 2,1 ) ]\frac{\partial {{w}^{b}}}{\partial \eta } -2\mu {{\tau }^{s}}}+
{[ {{T}_{44}}( 1,1 )‎+ ‎2{{T}_{44}}( 5,1 ) ‎+ ‎{{T}_{44}}( 2,1 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{4}}}}+
{[ {{T}_{44}}( 1,2 ) +2{{T}_{44}}( 5,2 ) +‎{{T}_{44}}( 2,2 ) ]\frac{{{\partial }^{4}}{{w}^{s}}}{\partial {{\eta }^{4}}}}+
   {{T}_{44}}( 1,3 )
$\end{center}


\end{document}

Or using breqn essentially the same input produces

\documentclass[12pt]{book}

\usepackage{breqn}

\usepackage{lipsum}
\begin{document}‎
How can I write equation beatifull. I want all equation the same of text width‎
\lipsum[1]

\begin{dmath*}
{[ {{T}_{44}}( 1,2 ) +2{{T}_{44}}( 5,2 )+‎{{T}_{44}}( 2,2 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\eta }^{4}}}}+
{[ {{T}_{44}}( 1,3 ) +2{{T}_{44}}( 5,3 )‎‎+‎{{T}_{44}}( 2,3 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{3}}\partial \eta }}+
{[ {{T}_{44}}( 1,4 )+2{{T}_{44}}( 5,4 )+{{T}_{44}}( 2,4 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial \xi \partial {{\eta }^{3}}}}‎+
{[ {{T}_{44}}( 1,5 )+2{{T}_{44}}( 5,5 )+{{T}_{44}}( 2,5 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{2}}\partial {{\eta }^{2}}}}+
{[ {{T}_{43}}( 1,1 ) +2{{T}_{43}}( 5,1 )‎+‎{{T}_{43}}( 2,1 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\xi }^{3}}}}+
{[ {{T}_{43}}( 1,2 )+2{{T}_{43}}( 5,2 )+{{T}_{43}}( 2,2 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\eta }^{3}}}}‎+
{[ {{T}_{43}}( 1,3 )+2{{T}_{43}}( 5,3 )+{{T}_{43}}( 2,3 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial {{\xi }^{2}}\partial \eta }}+ 
{[ {{T}_{43}}( 1,4 ) +2{{T}_{43}}( 5,4 )‎+ ‎{{T}_{43}}( 2,4 ) ]\frac{{{\partial }^{3}}{{w}^{b}}}{\partial \xi \partial {{\eta }^{2}}}}+
{[ {{T}_{42}}( 1,1 )+2{{T}_{42}}( 5,1 )+{{T}_{42}}( 2,1 ) )\frac{{{\partial }^{2}}{{w}^{b}}}{\partial {{\xi }^{2}}}}‎+
{[ {{T}_{42}}( 1,2 )+2{{T}_{42}}( 5,2 )+{{T}_{42}}( 2,2 ) ]\frac{{{\partial }^{2}}{{w}^{b}}}{\partial {{\eta }^{2}}}}+
{[ {{T}_{42}}( 1,3 )‎+ ‎2{{T}_{42}}( 5,3 )‎ +‎{{T}_{42}}( 2,3 ) ]\frac{{{\partial }^{2}}{{w}^{b}}}{\partial \xi \partial \eta }}+
{[ {{T}_{41}}( 1,1 )+2{{T}_{41}}( 5,1 )+{{T}_{41}}( 2,1 ) ]\frac{\partial {{w}^{b}}}{\partial \xi }}‎ +‎
{[ {{T}_{41}}( 1,1 )+2{{T}_{41}}( 5,1 )+{{T}_{41}}( 2,1 ) ]\frac{\partial {{w}^{b}}}{\partial \eta } -2\mu {{\tau }^{s}}}+
{[ {{T}_{44}}( 1,1 )‎+ ‎2{{T}_{44}}( 5,1 ) ‎+ ‎{{T}_{44}}( 2,1 ) ]\frac{{{\partial }^{4}}{{w}^{b}}}{\partial {{\xi }^{4}}}}+
{[ {{T}_{44}}( 1,2 ) +2{{T}_{44}}( 5,2 ) +‎{{T}_{44}}( 2,2 ) ]\frac{{{\partial }^{4}}{{w}^{s}}}{\partial {{\eta }^{4}}}}+
   {{T}_{44}}( 1,3 )
\end{dmath*}


\end{document}