1/1×3＋1/3×5+1/5×7+…+1/17×19+1/9×21=?
问题描述：
1/1×3＋1/3×5+1/5×7+…+1/17×19+1/9×21=?
答
1/1×3＋1/3×5+1/5×7+…+1/17×19+1/9×21
=0.5*(1/1-1/3+1/3-1/5+1/5-1/7+...+1/19-1/21)
=0.5*(1-1/21)
=10/21