旋转体的体积为 =兀 x2]2 丌b ∫( dx 2丌b d 2丌b 4丌ab 前页后页结束前页 后页 结束 a x x a b a x x a b V a a a a ( )d π π [ ] d 2 2 2 2 2 2 2   − − = − = − 旋转体的体积为 a x x a b a ( )d 2π 0 2 2 2 2 =  − 3 4π 3 2π 2 0 3 2 2 2 ab x a x a b a =       = −