# Is 'R' in impedance equation an AC or DC resistance?

I am using an impedance meter to measure impedance in complex form (R-jX) and an RLC meter to measure R & C values in an RC circuit. The value of DC resistance is equal to the R value in impedance equation. My question is whether the R in impedance an ac or dc resistance?

Very often, the $$\X\$$ component will be proportional to frequency so that in the limit as $$\\omega\to 0\$$, the impedance is $$\R\$$ making $$\R\$$ the DC resistance.
In other cases, $$\R\$$ also has some frequency dependence. Then the DC resistance is whatever value $$\R\$$ has when the frequency is 0.