心形线 r(θ) = a(1+cosθ) 极轴之上部分 0 ≤ θ ≤ π， 故所求旋转体体积 V = ∫ <0, π> (2π/3) r^3sinθ dθ = (2π/3)a^3 ∫ <0, π> (1+cosθ)^3sinθ dθ = -(2π/3)a^3 ∫ <0, π> (1+cosθ)^3 d(1+cosθ) = -(π/6)a^3[(1+cosθ)^4]<0, π> = (8π/3)a^3