题目

对函数x^2+y^2-y求重积分,其中积分区域D由y=x,y=2x及y=2围成

提问时间：2021-04-24

答案

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