6.二重积分计算的两种积分顺序 I=‖f(x,y)dxdy D:x1(y)≤x≤x2(y) D:y1(x)sy≤y2(x) c≤y≤d a<xsb y2(x) D D y(r) x b f(, ydx I f(x, y)dy x1(y) y1(x)0 y x c d y  d c dy D D: y1 (x)  y  y2 (x) a  x  b 0 y x I = a b y1 (x) y2(x) D x1 (y) x2(y) x    ( ) ( ) ( , )d y x y x I = f x y y 6. 二重积分计算的两种积分顺序 .  = D I f (x, y)dxdy    ( ) ( ) ( )d x y x y f x, y x D: x1 (y)  x  x2 (y) c  y  d