Many of the examples that I've included for this section on Op-Amps 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.
For the first couple of examples on the basic amplifier configurations, all of the working is shown directly in the page. Formatting all of the derivations and working, for HTML, got to be a bit tedious. I didn't really want to have to present everything formally. Irrespective, the working had to be done and in general I did it on paper. I figured that I could just scan it in, and present it as PDFs.
The actual pages here are linked from the equations in the Op-Amp 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!