u 故 L+1 (x2+y)y=‖()2 (u+v+2uv 2u- 2v)dudy du(u+v+2uv+2u-2v)dv 8 (2n2+4+=)d 8 3 310 1 2 2 1 1 ( ) [ ) ] 2 2 2 x y D u v u v x y dxdy dudv +  + − + = +  − 故 （   1 1 2 2 = ( 2 2 2 ) 8 D u v uv u v dudv + + + −  1 1 2 2 1 1 1 ( 2 2 2 ) 8 du u v uv u v dv − − = + + + −   u u du − = + +  1 2 1 1 2 (2 4 ) 8 3 = 1 3