%% formulation
\documentclass{standalone}
\usepackage{amsmath}
\usepackage{bm}
\usepackage{graphicx}
\usepackage{xcolor}
\begin{document}
\setlength{\abovedisplayskip}{2pt}
\setlength{\belowdisplayskip}{2pt}
\pagecolor{white}
\scalebox{2}{\parbox{0.1\textwidth}{%
\begin{align*}
\min_{u(t)} \quad & -x_1(t_f) \\
\text{subject to:} \quad & \dot{\bm{x}} = \begin{bmatrix} 0 & 1 \\ -k/m & 0 \end{bmatrix} \bm{x} +  \begin{bmatrix} 0 \\ 1/m \end{bmatrix} u \\
& \bm{x}(0) = (x_0,v_0) \\
& |u(t)| \leq u_{\max}
\end{align*}
}}
\end{document}

%% solution