计算1/1x3+1/3x5+1/5x7+……+1/99+101

1/(1×3)+1/(3×5)+1/(5×7)+……+1/(99×101) =1/2×(1-1/3)+1/2×(1/3-1/5)+1/2×(1/5-1/7)+……+1/2×(1/99-1/101) =1/2×(1-1/3+1/3-1/5+1/5-1/7+……+1/99-1/101) 【中间的约掉了】