Hi,
1)If i use an opamp with resistor feedback (for example in inverting configuration with gain -R2/R1), the output resistence seen by opamp is one resistor of R2 value? 2)for an opamp used in noninverting configuration (with gain 1+R2/R1), the output resistance seen by opamp is R1+R2? Thanks in advance
-- Yes
True if nothing else is connected to the op-amp output. Of course, what is an op-amp circuit for if not to drive other circuitry? Technically this is the not the "output resistance" but rather the load resistance. The output resistance is internal to the op-amp and has a low ohmic value. That low value is further reduced by the loop gain of the amplifier with feedback.
Excluding the external load, yes.
True with the same caveat.
Graham
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