叫=+n =0 解：由二维泊松公式： 4x,y,)= 2πat0J0 a2-2 aP-P =x(x(x+rcos0,y+rsine)=(x+rcos0)(x+y+rcos@+rsine) =x2(x+y)+2x(x+y)rcos0+(x+y)r2 cos20+xr(sin@+cos0) +2xr2(sin0+cose)cos+r(sin0+cose)cos20解：由二维泊松公式： 2 0 0 t t ( ), 0 u u x x y t        2 2 0 0 0 0 2 2 2 2 2 2 1 ( cos , sin ) 1 ( cos , sin ) ( , , ) + 2 2 at at x r y r x r y r u x y t rdrd rdrd a t a a t r a t r                                      2 0 0 2 2 2 1 ( cos , sin ) 2 at x r y r rdrd a t a t r                     2 0 ( ) u x x y t     2       x r y r x r x y r r        cos , sin ( cos ) ( cos sin ) 2 2 2 2 2 3 2 ( ) 2 ( ) cos ( ) cos (sin cos ) 2 (sin cos )cos (sin cos )cos x x y x x y r x y r x r xr r                      