This is not a homework, but while reading Floyd's book I can across something similar and decided to solve it! I just wanted to calculate the total impedance that the op-amp will see when connecting these 3 poles through a resistor of 6.2K to the non-inverting input to form an RC phase shift oscillator, also, I wanted to figure out the value of Rin to find the Rf required for the op-amp so that I can get an Av of 29 or more!

In this RC phase shift oscillator, I'm trying to calculate the total impedance of the 3 RC pairs!

Now the C3 and R3 have a Z3 of sqrt(Xc3^2 +R3^2) then we will have a parallel R2 with this Z3, can I directly add R2//Z3? as in R2//Z3 = Z2

Z2= 1/(1/R2)+(1/Z3) ????

if that was correct, we will face an Xc of C2 in series with the resulting Z2, can we add Xc2 with Z2 in series

Finally, should the Rin2 be included in the calculation ar all?

Thank you.