8. A spherical wave is a solution of the three-dimensional wave equation of the form u(r, t), where r is the distance to the origin (the spherical coordinate). The wave equation takes the form 2 . . u\" = (:2 (arr | u,) (\"spherical wave equation\"). r (a) Change variables I) = m to get the equation for v: v\" = czvrr. (b) Solve for 1) using (3) and thereby solve the spherical wave equat- ion. (0) Use (8) to solve it with initial conditions u(r, 0) = (Mr), 14,030) = 1,00\"), taking both (Mr) and 1M1\") to be even functions of r