Equation 9.11.38E5F90A48E44A

\begin{equation} A_ a=P_ a(s)\sigma _\psi +\frac{c_ a k(s)s^{n-1}}{P_ a(s)^{n-1}}(B_\psi -s\sigma _\psi ),\qquad A_ a^ n=c_ a\nu . \end{equation}