1/12+1/20+1/30+1/42+1/56+1/72= 等于多少?求1/12+1/20+1/30+1/42+1/56+1/72= 等于多少,

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1/12+1/20+1/30+1/42+1/56+1/72= 等于多少?求1/12+1/20+1/30+1/42+1/56+1/72= 等于多少,
1/12+1/20+1/30+1/42+1/56+1/72= 等于多少?
求1/12+1/20+1/30+1/42+1/56+1/72= 等于多少,

1/12+1/20+1/30+1/42+1/56+1/72= 等于多少?求1/12+1/20+1/30+1/42+1/56+1/72= 等于多少,
1/12+1/20+1/30+1/42+1/56+1/72
=1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)+1/(7×8)+1/(8×9)
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/3-1/9
=2/9

=1/3×4+1/4×5+……+1/8×9
=1/3-1/4+1/4-1/5+……+1/8-1/9
=1/3-1/9
=2/9

1/6+1/12+1/20+1/30+1/42 1/3-1/12-1/20-1/30-1/42 1／6+1／12+1／20+1／30+1／42 1/12+1/20+1/30+1/42+.+1/2450 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 1/2+1/6+1/12+1/20+1/30+1/42+1/56 简算 1/2+1/6+1/12+1/20+1/30+1/42+1/56简算, 1/12+1/20+1/30+1/42+1/56+1/72+1/90 简便运算：1/2+1/6+1/12+1/20+1/30+1/42+1/56 1+1/2+1/6+1/12+1/20+1/30+1/42的简便计算 2/1+6/1+12/1+20/1+30/1+42/1+56/1=? 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 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56怎么算 1+1/2+1/6+1/12+1/20+1/30+1/42=? 1/2+1/6+1/12+1/20+1/30+1/42+1/56 1/2-1/6-1/12-1/20-1/30-1/42-1/56等于多少