% https://www.latex4technics.com/

% formulation
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\begin{document}
\scalebox{2}{\parbox{0.1\textwidth}{%
\begin{align*}
\min_{u_1(t),u_2(t)} \quad & \int_{0}^{t_f} [-\xi_1 + (A_1u_i^2 +A_2u_2^2)] dt\\
\text{subject to:} \quad & \dot{\bm{\xi}} = \begin{bmatrix}
 s_1 - \frac{s_2\xi_2}{b_1+\xi_2} - \mu \xi_1 - k \xi_1 \xi_2 + u_1 \xi_1 \\
\frac{g(1-u_2)\xi_2}{b_2 + \xi_2} - c \xi_1 \xi_2\\
\end{bmatrix} \\
& \bm{\xi}(0) = \bm{\xi}_0 \\
& \xi_{1,\min} \leq \xi_1(t) \leq \xi_{1,\max} \\
& \xi_{2,\min} \leq \xi_2(t) \leq \xi_{2,\max} \\
& u_{1,\min} \leq u_1(t) \leq u_{1,\max} \\
& u_{2,\min} \leq u_2(t) \leq u_{2,\max}
\end{align*}
}}
\end{document}

% solution