Phasors are essential tool in circuit analysis.

Step-by-step instructions on how to solve circuits using phasors:
adopt cosine reference for generator voltage or current.
replace all impedances with their phasor expressions,
write KVL and KCL or use other Network Analysis techniques.
find the phasor expression for the required current or voltage.
calculate phasors
sketch the phasor diagram
multiply the phasor with
find the real part of the above expression to get the current in the time domain.

It is customary in Electrical Engineering to use for our time-domain signal, and we call these phasors ”cosine reference phasors.” If the generator in a circuit is , we first have to convert the sin function to a cosine. To do that, subtract from the phase of the sinusoid, because .