For those with a mathematical bent, alternatively stated, for the angle of
Zo to be zero, or for Zo to be purely resistive -

L * G = C * R

or

L / C = R / G

which relationship is derived from -

Zo = Squareroot( Z / Y )

Where line series impedance Z = R + j * Omega * L

and line shunt admittance Y = G + j * Omega * C

provided the angle of Z is equal to the angle of Y.

Which makes Zo = Ro + j * ZERO

QED
------
Reg, G4FGQ