1/2+1/6+1/12+1/20+...+1/90=?
来源:百度知道 编辑:UC知道 时间:2024/07/07 18:11:27
这是我在一本书上面遇到的题,不知道怎么做,请大家帮忙。
这个问题,首先要看到
1/2=1/(1*2)1-1/2
1/6=1/(2*3)=1/2-1/3
1/12=1/(3*4)=1/3-1/4
`
`
`
1/90=1/(9*10)=1/9-1/10
所以
1/2+1/6+1/12+1/20+...+1/90
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/6-1/7……+1/9-1/10
=1-1/10
=9/10
1/n*(n+1)=1/n-1/(n+1)
1/2+1/6+1/12+1/20+...+1/90
=1/1*2+1/2*3+1/3*4+1/4*5+...+1/9*10
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+...+(1/9-1/10)
=1-1/10
=9/10
每一项都是1/nx(n+1)
可分解为1/n-1/(n+1)
所以原式等于1-1/10=9/10
1/2+1/2-1/3+1/3-1/4+1/4-1/5……+1/9-1/10
=1/2+1/2-1/10
=9/10
=1-1/2+1/2-1/3+1/3-1/4+……+1/9-1/10
=1-1/10
=9/10
1/2+1/6+1/12+1/20+...+1/90
=1/1*2+1/2*3+13*4+……+1/9*10
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+……+(1/9-1/10)
=1-1/10
=9/10
(1/2) (1/4+1/6)=
1/2 ,1/3 ,1/6 /1/6 ,()
1/2+1/6+1/12+1/20+1/30
1/2+1/4+1/6+1/8+.......+1/n=?
-1/2-1/6-1/12-1/20-``````````````-1/4026042
1/2+1/6+1/12+......+1/1980+1/2070=?
1/2 1/6 1/3 2 ( ) 3 1/2 数字推理
1/2*4+1/4*6+1/6*8+.......+1/2006*2008
1/2*4+1/4*6+1/6*8+1/48*50
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=