∫∫(3-x-y)dxdy =∫[0-->1]∫[0-->2] (3-x-y) dydx =∫[0-->1] (3y-xy-1/2y²) |[0-->2]dx =∫[0-->1] (6-2x-2) dx =∫[0-->1] (4-2x) dx =(4x-x²) [0-->1] =3
