%% 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) + \frac{1}{2} \int_0^{t_f} u^2 \mathrm{d}t \\
\text{subject to:} \quad & \dot{\bm{x}} = \begin{bmatrix}x_2 \\ - x_2 + u \end{bmatrix} \\
& \bm{x}(0) = (0,0) \\
\end{align*}
}}
\end{document}

%% solution