Question

660 mH inductor has a reactance of 490 Ω and a frequency of 120 Hz. At what frequency would a 0.49 μF capacitor have the same reactance?

Answer 1

1)The formula for resonant frequency cannot be used here. Resonant frequency is the frequency at which the impedence of the circuit is minimum when the inductor and capacitor are together in a circuit. Here they are asking seperately about an inductor and a capacitor. They are not connected in a circuit. So you have to use the equations for reacance of both inductor and capacitor and equate them to find the frequency required for the capacitor.

2)