Non-Inverting Op-Amp Gain

Here the signal goes straight to the non-inverting input, and R_f with R_in form a divider that feeds a sample of the output back. Feedback forces that sample to equal the input, so the output must be larger by the divider's reciprocal: G = 1 + R_f/R_in. With 90 kΩ and 10 kΩ the gain is 10, in phase this time, and the input impedance is enormous, megohms to gigohms, because the signal only has to charge the op-amp's input capacitance.

That high input impedance is the reason this configuration dominates sensor front ends, where loading the source would corrupt the reading. The "one" cannot be removed: set R_f to zero and you get the unity-gain buffer, a follower with essentially infinite input and near-zero output impedance, which is the single most common op-amp circuit in existence. Attenuation, though, is impossible here: for gains below one, put a divider ahead of the buffer.