1⼀1×3+1⼀3×5+1⼀5×7+…+1⼀17×19+1⼀9×21=?

这道题不会做,请求朋友们的帮助
2025-06-21 19:14:41
推荐回答(1个)
回答1:

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