解法一：所求体积=2∫2πx√[16-(x-5)²]dx
=4π∫x√[16-(x-5)²]dx
=4π∫(4sint+5)*4cost*4costdt (令x=4sint+5)
=64π∫(4sint+5)cos²tdt
=640π∫cos²tdt
=320π∫[1+cos(2t)]dt
=320π[t+sin(2t)/2]│
=320π(π/2+0)
=160π²；
解法二：所求体积=2∫π[(5+√(16-y²))²-(5-√(16-y²))²]dy
=40π∫√(16-y²)dy
=40π∫4cost*4costdt (令y=4sint)
=320π∫[1+cos(2t)]dt
=320π[t+sin(2t)/2]│
=320π(π/2+0)
=160π².