A series circuit consists of an ac source of variable frequency, a $115-\Omega$ resistor, a $1.25-\mu F$ capacitor, and a $4.50-\mathrm{mH}$ inductor. Find the impedance of this circuit when the angular frequency of the ac source is adjusted to (a) the resonance angular frequency; (b) twice the resonance angular frequency; (c) half the resonance angular frequency.