\documentclass{article}
\usepackage[a4paper,landscape,margin=15mm]{geometry}
\usepackage{amsmath,graphicx}
\newcommand{\exprline}[1]{\par\noindent\begingroup\setbox0=\hbox{$\displaystyle #1$}\ifdim\wd0>\linewidth\resizebox{\linewidth}{!}{\box0}\else\box0\fi\endgroup\par\medskip}
\begin{document}
\noindent\texttt{L2HL\_2\_0235}\\
Version 5.3.1\\
\exprline{a_{0} = mchi_{1} mchipm_{1} - mchipm_{1} mchipm_{1} + \left(mchi_{1} + \frac{437582.32094343915}{mchi_{1}^{3}}\right) \left(-0.3173156761280718\right)}
\exprline{a_{1} = mchipm_{1} \frac{1}{mchi_{1}} \left(mchipm_{1} + mchipm_{1}\right) 437582.32094343915 \frac{1}{mchipm_{1} + mchipm_{1}}}
\exprline{a_{2} = \frac{\left(- mchipm_{1} + mchipm_{1}\right) \left(mchipm_{1} - 212895.46513659504\right)}{\left(-228741.5039211217\right) \frac{mchipm_{1}}{a_{1}}}}
\exprline{a_{3} = \left(\frac{mchi_{1}}{mchipm_{1}} + mchipm_{1} + 0.20566145903969044\right) \left(-471872.3014512357\right) \left(- mchipm_{1} + mchipm_{1} mchipm_{1}\right)}
\exprline{a_{4} = \frac{mchipm_{1} \left(mchipm_{1} + 18659320.149562974\right)}{mchipm_{1} \frac{1}{mchipm_{1} + \frac{mchipm_{1}}{mchi_{1} + mchipm_{1}}}}}
\exprline{a_{5} = mchipm_{1} \left(mchipm_{1} + mchipm_{1}\right) \left(-103.88372907417093\right) \frac{1}{mchipm_{1} + \frac{mchipm_{1}}{mchi_{1}}}}
\exprline{a_{6} = \frac{\left(- mchi_{1} - 1.0693912035373577 \cdot 10^{-7}\right) \left(mchipm_{1} - 212895.46513659504\right)}{a_{5}}}
\exprline{a_{7} = \frac{a_{4} + mchi_{1} - mchipm_{1}}{2.941411778360264 \frac{mchi_{1}}{a_{6} \left(- mchi_{1} + mchipm_{1}\right)}}}
\exprline{a_{8} = - (a_{7} - \left(mchipm_{1} + 0.47669089100900397 - \frac{228741.5039211217}{mchipm_{1}}\right)) + \frac{mchipm_{1}}{mchi_{1} \frac{- a_{2} - 103.88372907417093}{a_{3}}}}
\exprline{a_{9} = mchi_{1} \left(mchi_{1} + \frac{437582.32094343915}{mchipm_{1}^{3}}\right) \left(mchipm_{1} - 0.3173156761280718\right)}
\exprline{a_{10} = \frac{\frac{- a_{8} - 40.64579373720631}{a_{9} - mchipm_{1} mchipm_{1}} - 0.33437265106601716}{\left(-1\right) 52.91691590590071 \frac{1}{mchi_{1}}}}
\exprline{a_{11} = a_{10} + mchi_{1} \frac{1}{mchipm_{1} + 0.20566145903969044} \left(-471872.3014512357\right) - 1.4360175329545966}
\exprline{a_{12} = \frac{mchipm_{1} \left(mchipm_{1} + 18659320.149562974\right)}{mchi_{1} \left(mchipm_{1} + mchipm_{1}\right)}}
\exprline{a_{13} = - \frac{mchi_{1}}{\left(-228741.5039211217\right) \left(a_{12} - mchipm_{1}\right)} - \frac{103.88372907417093}{a_{11}}}
\exprline{a_{14} = \frac{mchipm_{1} \left(mchipm_{1} + 18659320.149562974\right)}{mchipm_{1} \left(mchipm_{1} + mchipm_{1}\right)}}
\exprline{a_{15} = \frac{mchi_{1} \left(- mchi_{1} - 1.0693912035373577 \cdot 10^{-7}\right)}{mchipm_{1} \left(- mchi_{1} + mchipm_{1}\right)}}
\exprline{a_{16} = - \frac{mchipm_{1} + mchipm_{1}}{-100749.11453079025} + \frac{mchi_{1}}{2.941411778360264 a_{15} \left(a_{14} - mchipm_{1}\right)}}
\exprline{a_{17} = - (- a_{16} + \frac{mchi_{1}}{mchipm_{1} a_{13} \left(- mchi_{1} + mchipm_{1} mchipm_{1}\right)}) - 0.33437265106601716 - \frac{40.64579373720631}{a_{0}}}
\exprline{s = \left(\frac{a_{17}}{\left(-1\right) 52.91691590590071 \frac{1}{mchi_{1}}} - 1.4360175329545966\right) 0.8293846149763463}
\end{document}