y = x² = 9 - x², 2x² = 9, x = ±3/√2二者交于A(3/√2, 9/2), B(-3/√2, 9/2)绕y 轴旋转, 用y做自变量较方便y = x², x = √yy = 9 - x², x = √(9 - y)y = 9/2上下部分的y处, 旋转体截面...