三、二重积分的性质死下 1.Jnkf(x,ya=k[1f(x,y)da(k为常数) 2.|f(x,y)±g(x,y)kda f(x,y)da±|ng(x,y)d 时半生 3. J f(,yodo=l f(x,y)do+l f(x, y)do (D=D1UD2,D1,D2无公共内点)三、二重积分的性质 D 1. k f (x, y)d ( k 为常数)    = + 1 2 3. ( , )d ( , )d ( , )d D D D f x y  f x y  f x y   = D k f (x, y)d