Editing Series and parallel circuits (section)

==Notation==
The value of two components in parallel is often represented in equations by the [[parallel (operator)|parallel operator]], two vertical lines (∥), borrowing the [[Parallel (geometry)#Symbol|parallel lines notation from geometry]].
<math display="block">R \equiv R_1 \parallel R_2 \equiv \left(R_1^{-1} + R_2^{-1}\right)^{-1} \equiv \frac{R_1 R_2}{R_1 + R_2}</math>

This simplifies expressions that would otherwise become complicated by expansion of the terms.  For instance:
<math display="block">R_1 \parallel R_2 \parallel R_3 \equiv \frac{R_1 R_2 R_3}{R_1 R_2 + R_1 R_3 + R_2 R_3} . </math>