小学奥数,十个分数和为1,分母均为小于100的偶数,分子均为1,且分母各不相同。求解。谢谢!最好有过程。
答案:3 悬赏:50
解决时间 2021-01-10 07:04
- 提问者网友:凉末
- 2021-01-09 20:59
小学奥数,十个分数和为1,分母均为小于100的偶数,分子均为1,且分母各不相同。求解。谢谢!最好有过程。
最佳答案
- 二级知识专家网友:过活
- 2021-01-09 22:14
解:1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10=1追问非常感谢!能说下过程么?追答解答:任意两个连续自然数倒数的积,就等于这两个连续自然数倒数的差。
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10
=1/﹙1×2﹚+1/﹙2×3﹚+1/﹙3×4﹚+1/﹙4×5﹚+1/﹙5×6﹚+1/﹙6×7﹚+1/﹙7×8﹚+1/﹙8×9﹚+1/﹙9×10﹚+1/10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10
=1.
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10
=1/﹙1×2﹚+1/﹙2×3﹚+1/﹙3×4﹚+1/﹙4×5﹚+1/﹙5×6﹚+1/﹙6×7﹚+1/﹙7×8﹚+1/﹙8×9﹚+1/﹙9×10﹚+1/10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10
=1.
全部回答
- 1楼网友:鱼芗
- 2021-01-10 00:12
hf010209的做法很好。
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10
=1/﹙1×2﹚+1/﹙2×3﹚+1/﹙3×4﹚+1/﹙4×5﹚+1/﹙5×6﹚+1/﹙6×7﹚+1/﹙7×8﹚+1/﹙8×9﹚+1/﹙9×10﹚+1/10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10
=1.
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10
=1/﹙1×2﹚+1/﹙2×3﹚+1/﹙3×4﹚+1/﹙4×5﹚+1/﹙5×6﹚+1/﹙6×7﹚+1/﹙7×8﹚+1/﹙8×9﹚+1/﹙9×10﹚+1/10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10
=1.
- 2楼网友:長槍戰八方
- 2021-01-09 23:37
1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(9*10)
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)
=1/2-1/10
所以要想再添上两个分数凑成1,只需再加上1/2+1/10即可
即(1/2+1/10)+(1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)
=(1/2+1/10)+(1/2-1/10)
=1/2+1/2
=1
【本题用到分数裂项知识:1/[n*(n+1)]=1/n - 1/(n+1)】
=1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(9*10)
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)
=1/2-1/10
所以要想再添上两个分数凑成1,只需再加上1/2+1/10即可
即(1/2+1/10)+(1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)
=(1/2+1/10)+(1/2-1/10)
=1/2+1/2
=1
【本题用到分数裂项知识:1/[n*(n+1)]=1/n - 1/(n+1)】
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