The Wave Equation

In this chapter, we review quickly the main properties of the solutions of the wave equation in ${\rm R}_x^n \times {\rm R}_t$, concentrating on the cases n = 2 and n = 3. Since we promised not to use distribution theory, we will make no attempt to prove the solution formulas in the most general context. It is understood that the functions we manipulate are supposed to allow the formula to be defined in the classical sense.