X(x=C T=0 10(1)=A0+B (x, t)=A+B n=0 naat naat u,(r, t)=(Acarat naat nZ T, (t)=A, cos+ B,sin +B si )COS n=1,2,3 t u(x, t)=Ao+ B(+2(A, cos"+B, sin /cos nAr naat 由初始条件: 4=9()4+∑4m=94=054=82 W(x)B+∑" nZ 2 nTc (2×d,B ds nl n x X x C  ( ) cos = 1 C. '' 0; 2 2 2 2 + T = l n a T  ( ) cos sin , l n at B l n at Tn t An n   = + ( , ) ( cos sin ) cos . l n x l n at B l n at un x t An n    = + n =1,2,3 T t A B t 0 0 0 ( ) = + u x t A B t n = 0 0 0 0 ( , ) = + ( , ) ( cos sin ) cos . 1 0 0 l n x l n at B l n at u x t A B t An n n    = + + +  = D. ( ) 0 u x t= = 由初始条件： sin ( ), 1 0 x l n x A An n   + =  = ( ) , 1 0 0   d l A l  = ( ). 0 u x t t= = sin ( ). 1 0 x l n x B l n a B t n n    + =  = ( )cos . 2 0       d l n n a B l n  = ( )cos ; 2 0      d l n l A l n  = ( ) , 1 0 0   d l B l  =