\input{_preamble}
\begin{document}
    \myeqs{
        \mathcal{C}^{(k)}(u) = \frac{\partial^k\mathcal{C}^{(0)}(u)}{\partial u^k} = \sum_{i=0}^{n-k} \mathcal{N}_{i,p-k}^{\boldsymbol{U^{(k)}}} (u)\, \boldsymbol{P}^{(k)}_i,\quad
        u \in [u_{p-k},u_{n+1-k}],\quad
        n > p
    }
\end{document}