Circuit reduction and simplification

The Laws of Circuit - you can learn and practice by just reading

WMD (Weapons of Mass Diminution)
: What and why are they? Delta-to-Wye transformation, Thevenin equivalent circuit, and source transformation. Why do we work on these topics. A simple answer is to simplify a complex circuit. In theory, we don't have to change any circuit in front of us. We can solve it by applying the 3 golden laws: Ohm, KCL, and KVL. Or we slightly revise them for the node voltage method or mesh current method, but the same 3 laws are applied. However, if we leave a complex circuit as it is, it would take more variables and more times. The simplification tools (Delta-to-Wye transformation, Thevenin equivalent circuit, and source transformation) along with series/parallel resistance rule, are to minimize a circuit so that we can easily manage to find a solution. So let's build a habit to look at a circuit and find a way to simplify one. When there is not more room for simplification, then you apply node voltage or mesh current, or just KCL and KVL for your solution process.