1/30+1/42+1/56+1/72简便算法是?

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1/30+1/42+1/56+1/72简便算法是?1/30+1/42+1/56+1/72简便算法是?1/30+1/42+1/56+1/72简便算法是?1/30+1/42+1/56+1/72=1/5*6

1/30+1/42+1/56+1/72简便算法是?
1/30+1/42+1/56+1/72简便算法是?

1/30+1/42+1/56+1/72简便算法是?
1/30+1/42+1/56+1/72
=1/5*6+1/6*7+1/7*8+1/8*9
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/5-1/9
=9/45-5/45
=4/45

1/30+1/42+1/56+1/72
=1/（5×6）+ 1/（6×7）+ 1/（7×8） + 1/（8×9）
=1/5 - 1/6 + 1/6 -1/7 +1/7 - 1/8 + 1/8 -1/9
=1/5 - 1/9
= 4/45

1/12+1/20+1/30+1/42+1/56+1/72 怎么简算? 1/30+1/42+1/56+1/72+1/90 1/30+1/42+1/56+1/72+1/90 1/30+1/42+1/56+1/72 简算 1/30+1/42+1/56+1/72简便算法 1/30+1/42+1/56+1/72＝简算1/30+1/42+1/56+1/72＝? 1/30+1/42+1/56+1/72= 30分之1+42分之一+56分之1+72分之一 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72 1/12+1/20+1/30+1/42+1/56+1/72+1/90 1/12+1/20+1/30+1/42+1/56+1/72+1/90 1/6+1/12+1/20+1/30+1/42+1/56+1/72 简便计算 1/2+1/6+1/20+1/30+1/42+1/56+1/72等于多少? 1/2+1/6+1/20+1/30+1/42+1/56+1/72等于几? 1/6+1/12+1/20+1/30+1/42+1/56+1/72 1/12+1/20+1/30+1/42+1/56+1/72+1/90=?