Exercise 9.3 A 5-stage RC phase shift oscillator

a)

An answer:
A is negative, so the combined phase shift of the 5 $\mathit{RC}$ filters should be -180 degrees. This leads to $\mathit{\angle stage}=-36^{\circ }$

b)

An answer:

$$\begin{array}{lll}\hfill {\omega }_{\mathit{osc}}=\frac{\mathit{tan}(36^{\circ })}{\mathit{RC}}& & \hfill \end{array}$$

c)

An answer:

$$\begin{array}{lll}\hfill A=-\sqrt{1+\mathit{tan}{(36^{\circ })}^2}& & \hfill \end{array}$$