i was wondering if anyone could point me towards any resources (including books, papers, and/or notes) that discusses and explicitly derives the fundamental solution to the radial wave equation. i have evans' PDE book, but it isn't contained there, and i've been having trouble searching for it. i'm really more concerned about the derivation and not the solution and how to use it. i'm also a little confused on what the radial wave equation is and its importance, so if you want to elaborate on that as well, it would be welcomed. thanks for the help.