=1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10
=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
=1/3-1/10
=7/30
【通项：
1/n(n+1)=1/n-1/n+1】
1/12+1/20+1/30+1/42+1/56+1/72+1/90
4个回答
相关问题
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1/12+1/20+1/30+1/42+1/56+1/72+1/90=?
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1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
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1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?
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1/20+1/30+1/42+1/56+1/72+1/90
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2\1-6\1-12\1-20\1-30\1-42\1-56\1-72\1-90\1
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1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=
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2/1＋6/1＋12/1＋20/1＋30/1＋42/1＋56/1＋72/1＋90/1
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1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90简便计算
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简算：1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
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简算6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1