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a$x_{j}(n)$

b $x_{j}^{'}(n)$

c$y_k(n)$

ab bc [angleA=90,angleB=90]cb From the signal flow graph we have the relationships

$$y_k(n) = A [ x^{'}_{j}(n) ]$$

and

$$x^{'}_{j}(n) = x_j(n) + B[ y_k(n) ]$$

Eliminating $x^{'}_{j}(n)$ we get

$$y_k(n) = \frac{A}{1-AB} [ x_j(n) ]$$