%% formulation
\documentclass{standalone}
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\begin{document}
\setlength{\abovedisplayskip}{2pt}
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\scalebox{2}{\parbox{0.1\textwidth}{%
\begin{align*}
\min_{u(t)} \quad & \int_{-\ell}^{\ell} r\sqrt{1+u^2} \mathrm{d}t \\
\text{subject to:} \quad & \dot{r} = u \\
& r(-\ell) = a \\
& r(\ell) = a
\end{align*}
}}
\end{document}

%% solution