D是△ABC,其中A(0,1),B(2,1),C(1,2), 原式=∫dx∫(2x-y)dy+∫dx∫(2x-y)dy =∫dx*(2xy-y^2/2)|+∫dx*(2xy-y^2/2)| =(1/2)∫(3x^2-2x)dx-(1/2)∫(5x^2-14x+8)dx =2/3.
