求下列旋转体的体积V: (Ⅰ)由曲线y=x2,x=y2所围图形绕x轴旋转所成旋转体; (Ⅱ)由曲线x=a(t-sint),y=a(1-cost)(0≤t≤2π),y=0所围图形绕y轴旋转的旋转体.

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问题 求下列旋转体的体积V:
(Ⅰ)由曲线y=x2,x=y2所围图形绕x轴旋转所成旋转体;
(Ⅱ)由曲线x=a(t-sint),y=a(1-cost)(0≤t≤2π),y=0所围图形绕y轴旋转的旋转体.

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答案(Ⅰ)如图3.2,交点(0,0),(1,1),则所求体积为 V=∫01π[ [*]-(x2)2]dx=π∫01(x-x4)dx [*] (Ⅱ)如图3.3,所求体积为 V=2∫02πayxdx=2π∫0a(1-cost)a(t-sint)a(1-cost)dt =2πa30(1-cost)2(t-sint)dt =2πa30(1-cost)2tdt-2πa3π(1-cost)2sintdt =2πa30(1-cost)2tdt [*] 2πa3π[1-cos(u+π)]2(u+π)du =2πa3π(1+cosu)2udu+2π2a3π(1+cosu)2du =4π2a30π(1+cosu)2du=4π2a30π(1+2cosu+cos2u)du=4π2a3[*] =6π3a3. [*]

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