Ia=(48^4-45^4)π/64 =（5308416-4,100,625）*0.0491=1207791*0.0491=59.302
Ib=(60^4-57.5^4)π/64=（12,960,000-10,931,289）*0.0491=2028711*0.0491=99610
惯性矩之比=Ib/Ia=1.68；说明在抗弯矩的能力时，后者强得多。
