Formula_4822

\[\begin{gathered}N_{v x}=\sum_{i=1}^{k} \lambda_{i} \frac{\partial f_{i}}{\partial x_{v}}, \quad N_{v y}=\sum_{i=1}^{k} \lambda_{i} \frac{\partial f_{i}}{\partial y_{v}}, \\N_{v z}=\sum_{i=1}^{k} \lambda_{i} \frac{\partial f_{i}}{\partial z_{v}} .\end{gathered}\]