s+3 Bs+c s3+3s2+6s+4s+1s2+2s+4 左右两边令s=0.32C 434 3 两边乘s,令→∞,0=2+B B3 4 2 4 3 0, C 左右两边令s = = + 两边乘 s 令s ＋B 3 2 , → ,0 = 1 2 4 3 2 3 6 4 3 3 2 2 + + + + + = + + + + s s Bs C s s s s s 3 1  C = 3 2  B = −