and I need to prove that this circuit has non-zero static dissipation.

Assume the inverter switches ideally at VDD/2, neglect body effect, channel length modulation and all parasitic capacitance.

Now When A=B= VDD, the voltage at node x is VX=VDD-VtN,but how can I prove analytically that there is no static power dissipation for inverter cmos? Because P=(Vdd^2)/Rp how can I compute equivalente resistance Rp for PMOS M2?