To start off the semester right, visit the Wikipedia and Mathworld websites and look up and understand:
Just explore the kinds of things you can find there - I'm discovering that these web references are rapidly becoming THE universal free textbook. It is actually amazing to watch it happen (and participate in it as time permits).
7.4, 7.6, 7.19, 7.21
Also, derive on your own all the principal results presented in
these online lecture notes. It is easy to read and see me do it. It is
not so easy to do it, even for me. Working through this, possibly
several times until you really ``get it'', will truly improve your
understanding of how everything works.