%% formulation
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\begin{document}
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\begin{align*}
\min_{u_1,u_2,u_3,u_4} \quad & \ \int_{0}^{t_f} [u_1 + u_2 + u_3 + u_4] \mathrm{d}t \\
\text{subject to:} \quad & \dot{\bm{x}} = \begin{bmatrix}
x_4 \\ x_5 \\ x_6 \\
[u_1 - u_2 + u_3 - u_4] \cos(x_3) \\
[u_1 - u_2 + u_3 - u_4] \sin(x_3) \\
\alpha [u_1 - u_2] - \beta [u_3 - u_4]
\end{bmatrix} \\
& \bm{x}(0) = (-10,-10,\pi/2,0,0,0) \\
& \bm{x}(t_f) = (0,0,0,0,0,0) \\
& 0 \leq u_1 \\
& 0 \leq u_2 \\
& u_1 + u_2 \leq 1 \\
& u_3 + u_4 \leq 1
\end{align*}
}}
\end{document}

%% solution