Circuit theory becomes much more elegant if you start to use complex numbers (conceptually, the Laplace transform [1]). But for an introductory lesson, this page seems nice, though perhaps a bit long.<p>[1] <a href="https:&#x2F;&#x2F;en.wikibooks.org&#x2F;wiki&#x2F;Circuit_Theory&#x2F;Laplace_Transform" rel="nofollow">https:&#x2F;&#x2F;en.wikibooks.org&#x2F;wiki&#x2F;Circuit_Theory&#x2F;Laplace_Transfo...</a><p>(If you grasp this reference, then you understand, I&#x27;d say, about 25% of what electrical engineering is about)