Resonance condition in series RLC circuit
It depends if RLC series resonator  is put in series or shunt in a circuit.

At series resonance \$X_L = -X_C\$ 

This  means that those impedances cancel leaving just the series resistance, R at resonance.  Then it becomes an R ratio divider with whatever else is at source or load. 

If RLC is a series resonator across Rs source impedance, it becomes a notch filter with R ratio defining depth of notch.







simulate this circuit &ndash; Schematic created using CircuitLab

The quality of L or C components is usually rated by ratio of X/R ratio = Q at some high frequency where Q= 100 is high, &lt;10 is low.