Greetings! I'm not very good at physics, so it was a bless to find this site while looking for tutorials about electronics. The problem is, I've been reading the whole day the chapter about Thevenin's Theorem, and I still don't get it completely. Could someone help me? I have no problem coming up with the equivalent resistance of the example, but the equivalent tension drop is a mistery. 11.2V seems to come from 28V minus 16.8V but... isn't there another battery on the circuit? Why doesn't it affect the outcome? Why isn't the equivalent tension drop, say, 7V - 4.2V = 2.8V? Thank you, DrJones.