Many of the examples that I've included for this section include formulae for calculating critical circuit parameters, or simply just illustrating the behaviour of a circuit. Sometimes this latter capability works better than any form of words.
The actual pages here are linked from the equations in the examples. You can see how and where the equations came from by clicking on those links, or you can just browse them here.
I must apologise in advance for my working. Certainly, if I think the working is wrong, I won't publish. Mathematically, there's usually more than one way to crack a nut. Often I find myself doing something the complicated way before I realise there's a more straightforward way. I've not insulated you from that here. Usually I'll say if I can see an easier way!