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) c≤y≤d ●●● x10) D x2(y) f(, y)dx (y)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