The Differential Equation $\frac { \partial ^ { 2 } u } { \partial x ^ { 2 } } + \frac { \partial ^ { 2 } u } { \partial y ^ { 2 } } = u$

Multiple Choice

The differential equation $\frac { \partial ^ { 2 } u } { \partial x ^ { 2 } } + \frac { \partial ^ { 2 } u } { \partial y ^ { 2 } } = u$ is Select all that apply.

A) linear
B) nonlinear
C) hyperbolic
D) elliptic
E) parabolic