解法2把D看成Y型域,则 xydx ]dy xX 2 D x=2 (2y-y Iy2-2解法 2 把D看成Y型域，则 2 2 1 2 2 2 1 3 2 1 4 2 2 1 [ ] [ ] 2 (2 ) 2 9 [ ] 8 8 y y xydx dy x y dy y y dy y y = =  = − = − =     D xyd  D O y x 1 2 y x = 2 x y =