12),习题1-21 (1-42)(s/-A) 4(Rs"+Rsn2+…+Rn2+R (1-43)△(s)=|s/-4=s"+as"+…+an1s+a R=A+al r=A+aa+al=artal (1-44 R=AR+al R AR 0=ARn-1+anI=△(A (A可逆) a.≠01 1 1 1 2 1 1 1 2 2 2 2 1 1 0 1 0 0 ( ) − − − − − − − −  = = + =  = + = + = + + = + = + = n n n n n n n n k k k R a a A AR a I A R AR a I R AR a I R A a A a I AR a I R A a I R I   (1-44) (A可逆) (1-42) ( ) ( ) 1 ( ) 2 1 2 1 1 0 1 − − − − − + + + +  − = n n n n R s R s R s R s sI A  (1-43) n n n n  s = sI − A = s + a s + + a − s + a − 1 1 1 ( )  (1-42),习题1-21