Impedance in R-C-L Circuits:

Impedance  within  an  R-C-L  series  circuit  is  equivalent  to  the  phasor  sum  of  inductive reactance, resistance and capacitive reactance in the below figure.

Figure: Series R-C-L Impedance-Phasor

Equations (8-12) and (8-13) are the mathematical representations of impedance in an R-C-L circuit.  Because the difference between X_L and X_C is squared, the sequence in that the quantities are subtracted does not affect the answer.

                                        (8-12)

                                   (8-13)