所求体积=∫π[a(1-cosθ)]²*a(1-cosθ)dθ
=πa³∫(1-cosθ)³dθ
=πa³∫(1-3cosθ+3cos²θ-cos³θ)dθ
=πa³∫[5/2-3cosθ+(3/2)cos(2θ)-(1-sin²θ)cosθ]dθ
=πa³[5θ/2-3sinθ+(3/4)sin(2θ)-sinθ+sin³θ/3]│
=πa³[(5/2)(2π)]
=5π²a³