Here, phase difference tanϕtan3π=RXL−XC=RXL−XC When, L is removed 3=RXCXC=3R When C is removed tan3π=3=RXLXL=R3 Hence, in resonant circuit tanϕϕ=R3R−3R=0=0 ∴ Power factor cosϕ=1 It is the condition of resonance therefore phase difference between voltage and current is zero and power factor is cosϕ=1.