3 l2-a2l1=0a(x,)=0 (x,1) Xx 0 0(x<x-6 V2(x0-8,x+O 0(x>x-) (x,1)=∑(Acos naat nat n7 +B, sin -s =00x,)=∑B naat nZA B ds 2/v 5 27v )nr(x0-6) nx0-8 (n)2a (n)2(osnr(x+δ) 4/h sIn (n丌)2a 47v (x,1)=∑ nto. nnat. na3. 0 2 utt − a uxx = u(x,t) x=0 = 0 u(x,t) x=l = 0 0 u t=0 =       − − +  − = = 0 ( ) ,( , ) 0 ( ) 0 0 0 0 0 0     x x v x x x x ut t (1) ( , ) ( cos sin )sin . 1 l n x l n at B l n at u x t An n n    =  +  = 0 u t=0 =  sin . 2 0 0 0       d l n n a v B x x n  + − = ( , ) sin sin . 1 l n x l n at u x t Bn n     = =      + = − − 0 0 cos ( ) 2 2 0 x x l n n a lv ] ( ) cos ( ) [cos ( ) 2 0 0 2 0 l n x l n x n a lv      − − + = − sin sin . ) sin sin 4 1 ( , ) 0 2 1 2 0 l n x l n at l n l n x a n lv u x t n         = = l n l n x n a lv     sin sin ( ) 4 0 2 0 =