.你分子分母全部写倒了
1/2=1/(1*2)=1-1/2
1/6=1/(2*3)=1/2-1/3
看出规律了吗
.
1/90=1/(9*10)=1/9-1/10
那么
原式=1-1/2+1/2-1/3+.+1/9-1/10=1-1/10=9/10
2/1＋6/1＋12/1＋20/1＋30/1＋42/1＋56/1＋72/1＋90/1
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相关问题
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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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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)2/1+6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1
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计算：1/2+1/6+1/12+1/20+/+1/30+1/42+1/56+1/72+1/90
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计算1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
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1/12+1/20+1/30+1/42+1/56+1/72+1/90=?
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1/12+1/20+1/30+1/42+1/56+1/72+1/90
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1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+.1/9900