来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/09/13 03:47:36
怎么答这两道题
![](http://img.wesiedu.com/upload/9/4e/94e637898f8198071335ea9edf5d1f3a.jpg)
1/(1×2)+1/(2×3)+1/(3×4)+...+1/(2004×2005)
=1-1/2+1/2-1/3+1/3-1/4+...+1/2004-1/2005
=1-1/2005
=2004/2005
1/(1×3)+1/(3×5)+1/(5×7)+...+1/(49×51)
=1/2×(1-1/3+1/3-1/5+1/5-1/7+...+1/49-1/51)
=1/2×(1-1/51)
=1/2×50/51
=25/51