%% 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 & \int_{0}^{t_f} |u| \mathrm{d}t \\
\text{subject to:} \quad & \dot{\bm{x}} = \begin{bmatrix} x_2 \\ u \end{bmatrix} \\
& \bm{x}(0) = (x_0,v_0) \\
& \bm{x}(t_f) = (0,0) \\
& |u(t)| \leq 1
\end{align*}
}}
\end{document}

%% formulation - alternative
% \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), u_{+}(t)} \quad & \int_{0}^{t_f} u_{+} \mathrm{d}t \\
% \text{subject to:} \quad & \dot{\bm{x}} = \begin{bmatrix} x_2 \\ u \end{bmatrix} \\
% & \bm{x}(0) = (x_0,v_0) \\
% & \bm{x}(t_f) = (0,0) \\
% & u(t) \leq 1 \\
% & -u(t) \leq 1 \\
% & -u(t) - u_{+}(t) \leq 0 \\
% & u_{+}(t) - u(t) \leq 0
% \end{align*}
% }}
% \end{document}

%% solution