1/1×2+1/2×3+1/3×4+.....1/2005×2006
来源:百度知道 编辑:UC知道 时间:2024/09/27 17:28:19
=??
1/n(n+1)=n+1-n / n(n+1) = 1/n - 1/n+1
把每项都展开了,写中间项就全约掉了.
最后得1-1/2006
比较常用的公式
1/1×2+1/2×3+1/3×4+.....1/2005×2006
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+.....+(1/2005-1/2006)
=1-1/2+1/2-1/3+1/3-1/4+...+1/2005-1/2006
=1-1/2006-------(中间的项都两两消去了)
=2005/2006
(1/2005-1)(1/2004-1)........(1/3-1)(1/2-1)
1+1/2+1/3+.....+1/n
1+1/2+1/3+...+1/100
1-1/2+1/3-.....-1/10
(1+1/2+1/3+1/4)×
(1-1/2)(1-1/3)(1-1/4)(1-1/5).....(1-1/1000)
1+1/(1+2)+1/(1+2+3)+...+1/(1+2+3+...+100)
1+1/(1+2)+1/(1+2+3)+-------+1/(1+2+3+----+100)
1+1/1+2+1/1+2+3+...+1/1+2+3...+2000
1+1/1+2+1/1+2+3.........+1/1+2+3.....100