where A1 and A2 are arbitrary constants. This result follows at once from the
linearity of the wave equation (5.23), i.e. each term in the wave equation is proportional
to y or one of its derivatives: it does not contain quadratic or higher-power
terms or product terms such as y(∂y/∂x). (Equations of this type are known as
linear equations.) We can see this as follows. Multiplying the first of the following
equations