Why At resonance the inductive reactance XL = 2πfL and the capacitive reactance XC = 1/(2πfC) are equal in magnitude, and because they act in opposite directions (one leads, one lags by 90 degrees) they cancel each other out. That leaves the circuit looking purely resistive, with no net reactance and zero phase angle between voltage and current. The frequency where this happens is f = 1/(2π√LC).
Watch out Resistance is not cancelled at resonance; only the two reactances cancel, and whatever resistance is present is exactly what remains to set the impedance and limit the current.
Resonance = XL = XC, reactances cancel, only R is left. Resistance never cancels.