nTX rla-x)= ∑ C sin nIx 4a 8a x(a-xsin -dx [(-1)”-1 (2k+1)丌 (2k+1)b 8a p (2k+1)z3 epr(2k+1)Ib )-exp( (2k+1)b 8a eb/(2k+1)丌b (2k+1)C(2k+1)zb )-exp( (2k+1)b C u(x,y)=x(a-x)+2(A, exp nny n7 nZX +B, exp[-1 sin1 ( ) sin n n n x x a x C a   = − =  2 2 3 3 3 3 0 2 4 8 ( )sin [( 1) 1] (2 1) a n n n x a a C x a x dx a a n k    = − = − − = − +  2 3 3 (2 1) 1 exp[ ] 8 (2 1) (2 1) (2 1) exp( ) exp( ) n k b a a A k k b k b a a     + − − = − + + + − − 2 3 3 (2 1) exp[ ] 1 8 (2 1) (2 1) (2 1) exp( ) exp( ) n k b a a B k k b k b a a     + − = − + + + − − 1 ( , ) ( ) { exp[ ] exp[ ]}sin n n n n y n y n x u x y x a x A B a a a     = = − + + − 