6.二重积分计算的种积分顺序r=/(x,)drdy D:x1()≤x≤x2() csy≤d x10y) x2() D f∫(x,y)dx x1(y) 囧0 y x c d y D x1 (y) x2(y) I = 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