%% 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_3(t_f)\\
\text{subject to:} \quad & \dot{\bm{x}} = \begin{bmatrix}
x_2 \\
u_1 \\
x_2^2/2 + x_3^2/2
\end{bmatrix} \\
& \bm{x}(0) = (0,1,0) \\
& -1 \leq u_1 \leq 1
\end{align*}
}}
\end{document}

%% solution