The phasor diagram is a name given to a sketch in the complex plane of the phasor voltages and currents throughout a specific circuit

8-2 Superposition, source transformation and Thevenin's theorem Superposition:

8-1 Nodal, mesh and loop analysis Nodal analysis:

We define the ratio of the phasor voltage to the phasor current as impedance

《电路》（英文版）7-6 Phasor relationships for、and R:

sinusoidal current or voltage at a given frequency is characterized by only two parameters an amplitude and a phase angle. The complex representation of the voltage or current is also characterized by these same two parameters

A real, an imaginary, or a complex forcing function will produce a real, an imaginary, or complex response, respectively. Instead of applying a real forcing function to obtain the desired real response, we apply a complex forcing function whose real part is the given real forcing function; we obtain a complex response whose real part is the desired real response

The effective value of any periodic current is equal to the value of the direct current which flowing through a resistance R, delivers the same power to r as periodic current does

The forced response The steady state responseThe(t) has been switched into the circuit at some remote U.=V. cos ot time in the past, and the natural response has died-out completely. The forced response(steady state response)must satisfy the differential equation

In either case, leading or lagging, we say that sinusoids are out of phase () if phase angles equal they are said to be in phase(同相)