二分之一加六分之一加十二分之一加二十分之一加三十分之一加四十二分之一加五十六分之一加七十二分之一?
3个回答
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1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
=(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)
=1-1/9
=8/9
=(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)
=1-1/9
=8/9
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原式=1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
=(6+2+1)/12+1/20+1/30+1/42+1/56+1/72
=3/4+1/42+1/56+1/72+5/60
=(42+1)/56+1/42+1/72+1/12
=43/56+1/42+(1+6)/72
=(43x6+8)/336+7/72
=266/336+7/72
=(266x6+7x28)/2016
=(1596+196)/2016
=1792/2016
=56/63
≈0.889
=(6+2+1)/12+1/20+1/30+1/42+1/56+1/72
=3/4+1/42+1/56+1/72+5/60
=(42+1)/56+1/42+1/72+1/12
=43/56+1/42+(1+6)/72
=(43x6+8)/336+7/72
=266/336+7/72
=(266x6+7x28)/2016
=(1596+196)/2016
=1792/2016
=56/63
≈0.889
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