Impedance and resonant frequency derivation
You are both wrong. The passive parts can have 2 resonances if the source is changed to add series R.

Since there is no resistance in the ideal parts shown, and the Voltage source makes the circuit voltage constant thus only series current resonance can affect changes. So C2 has no effect here.

But is this a trick question to find Zeq. regardless of source?


one needs a high series R load in practise to see the parallel resonance effect of C2  (e.g. Colpitts, or Pierce Osc use high input Z.

As we know with unknown R's the way to find its value is  to insert a series R of equal value. Here the source is 0 ohms so no parallel resonance can be seen with voltage.


Impedance is pure reactance with 3 distinctive reactive parts, so we expect a 3rd order effects.


there are two resonant loads , one parallel and one series. 

This is the standard configuration of all crystal and ceramic resonators but without ESR shown.

The series resonance (notch Z) occurs 1st from LC1 and followed closely by the parallel resonance from both C1, C2 and the spacing depends on the ratio of sqrt of C1/C2


Try again. Zeq= Z(C2) // {Z(L)+Z(C1)}