As+b Cs+D R(S)= 6s2+4s+3s2+1 4 A B C D 25 25 25 25 r(t)=-ce3 cos,iot+ e sin t+ V1825 V18 自由,着态 cost+-sin t 25 25迫,稳态6 4 3 1 ( ) 2 2 + + + + + + = s C s D s s As B R s 25 7 , 25 1 , 25 4 , 25 6 = = = − A = B C D = − + + − − r t e t e t t t 18 7 sin 25 1 18 7 cos 25 1 ( ) 3 1 3 1 t sin t 25 7 cos 25 1 + 自由,暂态 强迫,稳态