V=0 x=0,x=a,y=0,d=0 y=b,d=U 由边条得 Φ(x,y2)=∑4sin-sh n7 y n=1 =∑41sizx, sh nzt ∫Un nIx sin =「sm2(x-), sh -dx( ) 2 0 1 0 1 2 0 0 0 0 0, , 0, 0 , , , sin sin sin sin ( ) n n n n a a n x x a y y b U n x n y x y z A sh a a n x n b U A sh a a n x n x n b U dx A sh dx a a a         =  =   =   = = =  =  =  =   =  =  =      由边条得