Transform the one-dimensional wave equation (3.4) into a system of PDE of the first order, such as (3.26). Find the eigenvalues of matrix \(\boldsymbol{R}\), and determine the type of the system. Does it agree with the type of (3.4) as an equation of second order? Hint: Introduce new variables \(v=\partial u / \partial t\) and \(w=a \partial u / \partial x\).