I do not understand what you want. I already did everything. I got that on any very small gap (dX-->0) Field constantly. And he wrote what is equal. The intensity of the field was equal to the voltage on the plates, divided by the distance between the plates. Your task is solved!

Ou you are right. Thank you for your patience and help

 

Yes, everything I wrote at the very beginning is a lie. I studied at the university 40 years ago (and even more so in school) and much has forgotten. I rummaged a bit on the Internet and found the formula: E=Q/(epsilon0*epsilon*S).
This is the formula for the strength of a flat capacitor. It includes the charge of the capacitor and the area of the capacitor. The capacitor charge is determined by the voltage on the capacitor and its capacitance. The capacitance of the capacitor is determined by the area of the electrode and the distance between the plates. Using these three relationships, I received that the strength of the field does not depend on the functional dependence of the dielectric permeability on distance.

I solve my assignment as you showed me, and my teacher said is "full of small, unnecessary mistakes", and failed me..