s+1 k2=(s+2)F(s)=22-1)/=212 s+1 k3=(-1)F() 2s(s+2)3 得F(S)=-+-24+ ss+ 2s-1 f(1)=L[F(s) e+-et≥0 闪四 西南交通大学西南交通大学 12 1 2 ( 1) 1 ( 2) ( ) 2 2 2 = - - + = + s=- = s=- s s s k s F s 3 1 2 ( 2) 1 ( 1) ( ) 3 1 1= + + = - s= = s= s s s k s F s 得 2 1 ( ) 3 1 12 1 4 1 - + + - + - = s s s F s 0 3 1 12 1 4 1 ( ) [ ( )] 1 2 = = - - + ³ - - f t F s e e t t t L