1/1*3+1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15+1/15*17+1/17*19+1/19*21
答案:5 悬赏:50
解决时间 2021-04-28 11:50
- 提问者网友:虛偽丶靜
- 2021-04-27 15:09
1/1*3+1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15+1/15*17+1/17*19+1/19*21=
最佳答案
- 二级知识专家网友:眠于流年
- 2021-04-27 15:55
原式=(1-1/3)×1/2+(1/3-1/5)×1/2+(1/5-1/7)×1/2……
+(1/19-1/21)×1/2
=(1-1/3+1/3-1/5+1/5-……+1/19-1/21)×1/2
=(1-1/21)×1/2
=10/21
100对!!!!!!!!!
+(1/19-1/21)×1/2
=(1-1/3+1/3-1/5+1/5-……+1/19-1/21)×1/2
=(1-1/21)×1/2
=10/21
100对!!!!!!!!!
全部回答
- 1楼网友:甜野猫
- 2021-04-27 19:35
1/2*[(1-1/3)+(1/3-1/5)+......(1/19-1/20)]
=1/2(1-1/20)
=19/40
- 2楼网友:青灯壁纸妹
- 2021-04-27 18:18
1/1*3+1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15+1/15*17+1/17*19+1/19*21
=(2/1*3+2/3*5+2/5*7+2/7*9+2/9*11+2/11*13+2/13*15+2/15*17+2/17*19+2/19*21)*1/2
=(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15+1/15-1/17+1/17-1/19+1/19-1/21)*1/2
=(1-1/21)*1/2
=20/21*1/2
=10/21
- 3楼网友:晚安听书人
- 2021-04-27 17:41
1/1*3+1/3*5+1/5*7+1/7*9+1/9*11+1/11*13+1/13*15+1/15*17+1/17*19+1/19*21
=2×(1-1/3+1/3-1/5+1/5-1/7+...+1/19-1/21)
=2×(1-1/21)
=40/21
- 4楼网友:情战凌云蔡小葵
- 2021-04-27 17:26
1/2*[(1-1/3)+(1/3-1/5)+......(1/19-1/21)]
=1/2(1-1/21)
=10/21
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