Answer
The wave equation is a partial differential equation that describes the propagation of waves. It is named after Jean le Rond d'Alembert, who first derived it in 1747. The wave equation has the form: ``` ∂²u/∂t² = c²(∂²u/∂x² + ∂²u/∂y² + ∂²u/∂z²) ``` where u is the wave function, t is time, and x, y, and z are the spatial coordinates. The constant c is the wave speed.