n(x,1)=lim∑w(x,r) Aτ→0r=0 则,瞬时力所引起的振动的定解问题为: Mn-a2=0<t<+△τ W==0 Mnl==f(x,T)△τ 设:w(xt,r)=vxt,r)△ v av=0 <4 =x=0 ==f(x,r)<6>å D ® = = t u x t w x t 0 0 ( , ) ( , ; ) lim t t t 则，瞬时力所引起的振动的定解问题为： ï î ï í ì = D = - = < < + D = = t t t t t t t | ( , ) | 0 0 2 w f x w w a w t t t t tt xx 设： w(x,t;t ) = v(x,t;t )Dt < > < > < > ï î ï í ì = = - = = = 6 5 4 | ( , ) | 0 0 2 t t t v f x v v a v t t t tt xx