Calculating Resistance

I guess you should call it impedance. "Z"

Z= ( R^2 + Xc^2 )^1/2

Xc = 1/(2*pai*f*C)

f is frequency

C capacitance

Xc capacitive reactance

R resistance

Z is Impedance

If you are talking about the feedback RC network of and op amp, then the total impedance in the Laplace domain of R || C is R/(RCs +1); So if you where trying to make a low pass filter the cutoff frequency would be fc=1/(2*pi*R*C). Hope this helps.

Would you please elaborate? For example, is the 51k resistor on the inverting input with the 0.005 μF cap as the sole feedback element, ie, are we talking about an integrator? If not, would you please describe the circuit configuration in more detail?

-e

Right. What is the diagram (or "configuration with C').

Also R f (feedback resistance) is a function of desired amplification factor