R(s) H(s) R(s) G2(s) R(s) -G(s)}∞-(5)} H2(s) H1(s) 图251习题28结构图 (a) C(s) G1+G2 C(s) G,G2+G R(s)1+(G1+G2)(G3-G4 R(s)1+G2(H1-H2) s) (s) R(s) 1G2(s) H(s)(e) (f) (g) 图 2-51 习题 2-8 结构图 【解】 (a) 1 2 1 2 3 4 ( ) ( ) 1 ( )( ) C s G G R s G G G G + = + + − , (b) 1 2 2 2 1 2 ( ) ( ) 1 ( ) C s G G G R s G H H + = + − ( ) 2 G s H(s) R(s) C(s) ( ) 1 G s G(s) H(s) R(s) C(s) B(s) 10 ( ) 3 G s ( ) 1 H s R(s) C(s) ( ) 1 G s ( ) 2 H s ( ) 2 G s ( ) 2 H s ( ) 3 G s ( ) 1 H s R(s) C(s) ( ) 1 G s ( ) 2 G s ( ) 3 G s H(s) R(s) C(s) ( ) 1 G s ( ) 2 G s