D={(x,y)q1(x)≤y≤q2(x), y=p,(x) a<xsb x=y(y D B D={(x,y)v1(y)≤x≤v2(y) xiv() c≤y≤a Cy=p(r) b 00 ∫d=4 2(y)0Q ax v1(y)ax dx=(Olv2(v),yl-Olv,(),y1)dy L 2lv2(),yldy-L2lv,(), yldy C L o(, y)dy Q(x,y)+」Q(x,y)y CBE =v2(y)yp-gowv(y)y图四y x o a b D cd ( ) y = 1 x ( ) y =  2 x A B C E ( ) 2 x =  y ( ) 1 } x = y {( , ) | ( ) ( ), 1 2 a x b D x y x y x   =     } {( , ) | ( ) ( ), 1 2 c y d D x y y x y   =    dx xQ dxdy dy xQ yy dc D     =  ( ) ( ) 21  =  − dc {Q[ ( y), y] Q[ ( y), y]}dy  2  1 =  − dc dc Q[ ( y), y]dy Q[ ( y), y]dy  2  1 LQ(x, y)dy   = + CBE EAC Q(x, y)dy Q(x, y)dy =  dc Q[ ( y), y]dy  2 −  dc Q[ ( y), y]dy 1