%% 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_1(t)} \quad & -x_1(t_f) \\
\text{subject to:} \quad & \begin{bmatrix} \dot{x}_1 \\ \dot{x}_2 \\ \dot{x}_3 \\ \dot{x}_4 \end{bmatrix} = \begin{bmatrix}
a \cos(u_1) \\ a \sin(u_1) \\ x_1 \\ x_2
\end{bmatrix} \\
& 0 \leq x_4(t) \\
& \bm{x}(0) = \bm{0} \\
& x_2(t_f) = 0 \\
& x_4(t_f) = h
\end{align*}
}}
\end{document}

%% solution