Chapter 12.1, Problem 23E

To determine

To classify: The partial differential equation $\frac{{\partial }^{2}u}{\partial x^2}+2\frac{{\partial }^{2}u}{\partial x\partial y}+\frac{{\partial }^{2}u}{{\partial }^{2}y}+\frac{\partial u}{\partial x}-6\frac{\partial u}{\partial y}=0$.