Series and Parallel RLC Circuits

Series RLC:

$Z = R + j\left(\omega L - \frac{1}{\omega C}\right)$

The circuit is inductive when $X_L > X_C$ (current lags) and capacitive when $X_C > X_L$ (current leads).

Parallel RLC — add admittances:

$Y = \frac{1}{R} + j\left(\omega C - \frac{1}{\omega L}\right)$

Draw the impedance triangle ($R$, $X$, $Z$) to visualise the phase angle.