It can’t be shown often enough - the most elegant building block in electronics:
In an ideal op-amp …
the V+ and V- inputs have infinite resistance there is zero current into and out of both V+ and V- if V+ is above V-, however slightly, then Vout will be Vs+ if V- is above V+, however slightly, then Vout will be Vs- when V- is V+, Vout will be halfway between Vs+ and Vs- the gain of the amplifier is infinitely large when V+ and V- change by the same amount, Vout stays the same as long as in-/outputs are within Vs+ and Vs-, changes to Vs+ and Vs- have no effect the behaviour is identical for any frequency, temperature, and time span Back on earth, things are a bit less rosy.
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