As phase angle contribution by capacitor and inductor are equal in magnitude, so XL=Xc⇒ωL=ωC1 It means that the RLC circuit is in resonance condition. So, impedance at resonance, Z=R2+(XL−XC)2=R2+(XL−XL)2=R2=R Thus, power factor, cosϕ=ZR=RR=1