计算二重积分∫∫D(x^2+y^2-x)dxdy,其中D由y=2,y=2x,y=x围城的闭区域
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先积x,∫∫ (x²+y²-y)dxdy
=∫[0--->2]dy∫[y/2--->y] (x²+y²-y)dx
=∫[0--->2] (1/3x³+xy²-xy) |[y/2--->y]dy=∫[0--->2] (1/3y³+y³-y²-(1/3)(y/2)³-y³/2+y²/2) dy
=∫[0--->2] [(19/24)y³-(1/2)y²] dy
=[(19/96)y⁴-(1/6)y³] |[0--->2]=11/6