1/12+1/20+1/30+1/42+1/56+1/72+1/90
=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
（将1/4~1/9消去)
给分啊~!
1/12+1/20+1/30+1/42+1/56+1/72+1/90=?
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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