near (400/Pi)*li, You are right.

來源: 於 2010-05-26 15:14:20 [舊帖] [給我悄悄話] 本文已被閱讀：次

x=r(1-sint)
y=r(1-cost)
ds=2^.5r(1-cost)^.5dt,s=Intg(2^.5r(1-cost)^.5dt)from 0 to 2Pi= 8r, so (100/2Pi*r)*8r=(400/Pi)li.