z=∫(x,y) A(x)=f(x,y)小y 0(x) 所以: b b. rp2() 和=4)=xy)yx D a p1 上一页下一页返回y Z ( x ) 1 ( x ) 2 z = f ( x , y ) =  ( ) ( ) ( ) ( , ) xx A x f x y dy 21   = D ba f(x,y)dxdy A(x)dx 所以： f(x.y dy dx ba (x) (x) [ ) ] 2 1   = 