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$ L= \left(u^S\right)^{0.5}\left(u^T\right)^{0.5} - \lambda\left(u^S+u^T-9.9\right)$\vspace{1ex}
\begin{empheq}[left=\implies\empheqlbrace]{flalign}
  0=\diff{L}{u^S}&= 0.5\left(u^S\right)^{-0.5}\left(u^T\right)^{0.5}-\lambda  &\\
  0=\diff{ L}{u^T}&= \left(u^S\right)^{0.5}0.5\left(u^T\right)^{-0.5}-\lambda\\
   u^S + u^T &= 9.9
\end{empheq}

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