Doesn't varying R2 just vary the gain by which the DC input voltage is
multiplied to produce the output? So if R2 varies sinusoidally at
frequency f, the output will be a sine wave at frequency f.
Vout = Vin*R2/R1
Within the range where the op-amp has infinite gain, sure.
At 1 MHz, I doubt it.
He's talking about R2 variations at high frequencies, getting Bode
plots. Under those conditions, the assumption falls through. Think
about what happens at the output node when the op-amp is totally
unresponsive (no current from its output pin, take the op-amp out of
the circuit).
Andy
