偏微分算符

\begin{equation} \left( \frac{\partial}{\partial{x}} + 1 \right) ^2 = \frac{\partial^{2}}{\partial{x}^{2}} + 2 \frac{\partial}{\partial{x}} + 1 \end{equation}

\begin{equation} \left( \frac{\partial}{\partial{x}} + \frac{\partial}{\partial{y}} \right) ^2 = \frac{\partial^{2}}{\partial{x}^{2}} + \frac{\partial^{2}}{\partial{y}^{2}} + 2 \frac{\partial^2 }{\partial x \partial y} \end{equation}