ft f060+ k=0 07 f(0 当∧z→>0 △r2△z k△z t) oim f(t)= ∑f(k△)(t-k△)△乙 △→>0k=0 △z2Xz k /o=(y)0026bf(t) 0 t f(0) f0 f1 f2  fk    2 k 0 f(t) t  2 k =   −  − − +  n k f t f k U t k U t k 0 即 ( ) (  )[ (  ) ( ( 1)  ] 当 → 0 =  −    → = n k f t f k t k 0 ( ) ( ) 0 lim ( )      ( ) ( ) ( ) ( ) ( ) …2.6-1 0 f t f t d f t t t  =   −  =  