Formula_15289

\[\begin{aligned}L u=\sum_{i, j=1}^{n} a_{i j}(x) \frac{\partial^{2} u(x)}{\partial x_{i} \partial x_{j}}+\sum_{i=1}^{n} b_{i}(x) \frac{\partial u(x)}{\partial x_{i}}+ \\+c(x) u(x)=f(x),\end{aligned}\]