What happens when inductive and capacitive reactance are equal in a series LC circuit?
Why In a series LC circuit the inductive and capacitive reactances are opposite in sign, so when XL = XC they cancel exactly. What remains is only the small resistance of the components, so the total impedance drops to a minimum and current peaks. That condition is series resonance, at f = 1/(2*pi*sqrt(LC)).
Watch out Very high impedance at resonance describes a parallel LC circuit (a tank), where the circulating current between L and C makes the circuit look like a large impedance to the source. The mean-of-L-and-C choices are nonsense; impedance is not an average of henries and farads.
Series resonance = Small impedance, big current. Parallel resonance = the opposite.