令:W(x,t)=A(t)x+B(t)…(6) W0=4,(0…(4) →40)=7,0-40lB0=40 Wx=L=4(t)…(5) mx)=2a0-4x+40 于是得:=r+令: 于是得到: 0 1( ) (4) W u t x 2 ( ) (5) W u t x L W x t A t x B t ( , ) ( ) ( ) (6) ( ) ( ), ( ) ( ) 1 ( ) 2 1 1 u t u t B t u t L A t 2 1 1 1 W x t u t u t x u t ( , ) ( ) ( ) ( ) L 2 1 1 u u u V u x L