For Proof of the Thevenin theorem:

http://tcts.fpms.ac.be/cours/1005-01/equiv.pdf www.eng.fsu.edu/~depriest/EE3003Lab/circuit_theorems.ppt http://fr.wikipedia.org/wiki/Th%C3%A9or%C3%A8me_de_Th%C3%A9venin