②若D关于y轴对称 (1)当f(-x,y)=-f(x,y)时I=0 (2)当f(-x,y)=f(x,y时1=2∬f(x,y)c D1=(x,y(x,y)∈D,x≥0} ③若D关于原点对称 (1)当f(-x,-y)=-f(x,y时I=0 (2)当f(-x,-y)=f(x,Jy)时I=2f(x,y)dd D3={(x,y)∈D,x≥0，y≥0}②若 D 关于 y 轴对称 (1)当f (−x, y) = − f (x, y)时 I = 0 (2)当f (−x, y) = f (x, y)时  = 1 2 ( , ) D I f x y dxdy D1 = (x, y)(x, y) D, x  0 ③若D关于原点对称 (1)当f(−x,− y) = − f(x, y)时 I = 0 (2)当f (−x,− y) = f (x, y)时  = 3 2 ( , ) D I f x y dxdy ( , ) , 0, 0 D3 = x y  D x  y 