say i have a circuit like this, i understand how to derive the expressions for critically,under and over-damped. These are the roots of characteristic equation Now my question is, to get expression for LC circuit, we can simply make R=0. however, what happen if i want to make it RL, or RC? Actually, this is a question that bothers me quite some time, it seems like i just need to get rid of the terms that contain L or C, otherwise the terms will be infinite. also, if either L or C is missing, there is no resonant frequency?