6.二重积分计算的两种积分顺序r=』y(x;ddy D:x1()≤x≤x2() csy≤d x10y) x2() D f∫(x,y)dx x1(y) 囧D: x1 (y)  x  x2 (y) c  y  d I =    ( ) ( ) ( )d x y x y f x, y x 0 y x x1 (y) x2(y) D c d y  = D I f (x, y)dxdy 6. 二重积分计算的两种积分顺序