t=0 ∑ A, cos a,x=0 0(E<x≤D) n aB co 0(E<x≤D) t|t=0 l/ps(x≤) n=1 /pE(x≤E) sm、E B coS,xdx= N2√A,apE N n 1/N2 2 h+1(2h2+1) B a, ap h+l(a,h+ 2 (x,t)= sIn at cos aDa√nh+l(xh2+1)0 u t=0 = cos 0. 1  =  = A x n n n  . / ( ) 0 ( ) 0       = =    I x x l ut t .. / ( ) 0 ( ) cos 1        =  =      I x x l aB x n n n n An = 0              N a I N a I xdx I N a B n n n n n n n n n n 2 0 2 0 2 sin cos 1 → =  = → ( 1) 2 1/ 2 2 + + = h l h N n n  ( 1) 2 2 + + = a h l h I B n n n    sin cos . ( 1) 2 1 1 ( , ) 1 2 at x a h l h I u x t n n n n n        = + + =