Impedance Triangle -->   A triangle which gives the relation between reactance ,resistance and Impedance is known as Impedance triangle

Impedance of LCR circuit

Z = R² + (X_L – X_C)²)^1/2

= (R² + (2πf.L – 1/2πf.C)²)^1/2

If f = 0           Z = ∞

f = ∞             Z = ∞  

If X_L = X_C        Z = R (min value of Z)

Z min = R when X₂ = X_C

X_L = X_C

2πfL = 1/2πfC

f = 1/2π(LC)^1/2 = f₀

f₀ = 1/2π(LC)^1/2

f₀ --> Resonant frequency

(I_rms)_max = V/R = V/Z_min

I_max = V/Z_min