Bob Eldred wrote:

Impedance varies with frequency if there are reactive components, L's and
C's.

That is not always true.

Take
1) A resistor of resistance R in series with a capacitor of capacitance C.

2) Another identical resistor of resistance R, but in series with an
inductor L.

Make R=sqrt(L/C)

and put 1 and 2 in parallel and measure the impedance across that
combination. The impedance is always R, and is independent of frequency.

A useless fact I would admit!!