作业帮计算题 1/2+1/6+1/12+1/30+1/42
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计算题 1/2+1/6+1/12+1/30+1/42
计算题 1/2+1/6+1/12+1/30+1/42
计算题 1/2+1/6+1/12+1/30+1/42
1/2+1/6+1/12+1/20+1/30+1/42
= 1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
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1/2+1/6+1/12+1/30+1/42
=1/2+1/6+1/12+1/20+1/30+1/42-1/20
=（1-1/2）+（1/2-1/3）+（1/3-1/4）+（1/4-1/5）+（1/5-1/6）+（1/6-1/7）-1/20
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7-1/20
=1-（1/...
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1/2+1/6+1/12+1/30+1/42
=1/2+1/6+1/12+1/20+1/30+1/42-1/20
=（1-1/2）+（1/2-1/3）+（1/3-1/4）+（1/4-1/5）+（1/5-1/6）+（1/6-1/7）-1/20
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7-1/20
=1-（1/2-1/2）-（1/3-1/3）-（1/4-1/4）-（1/5-1/5）-（1/6-1/6）-1/7-1/20
=1-0-0-0-0-0-1/7-1/20
=6/7-1/20
=113/140
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