when I'm studying Op-amp amplifier  , in the derivations we always take voltage difference between inverting input and non inverting input is approximately zero  . But I can'f find any explanation "why" ? This consideration is always taken for both inverting amplifier and non inverting amplifier  .

... ... Why this voltage difference always remain approximately zero  ? any explanation  ?

I found a lecture of my senior's professor's where he said that "as ideal op-amp's input impedance infinite so it's positive terminal and negative terminal are virtually short. I mean very little voltage drop which can be neglected "

I can't understand why very high (practical case) input impedance may cause very little voltage drop  .

In studying the OpAmp amplifier, the derivations always take the voltage difference between the inverting- and non-inverting input to be approximately zero. But I can't find any explanation "why". This consideration is always taken for both the inverting- and non-inverting amplifier.

Why is this voltage difference always approximately zero? Any explanation?

I found a lecture of my senior professor, where he said that "as the ideal op-amp's input impedance is infinite, its positive- and negative terminal are virtually short. I mean very little voltage drop which can be neglected."

I can't understand why a very high (practical case) input impedance may cause a very little voltage drop.