1/2-1/6-1/12-1/20-1/30-1/42
=1/3-1/12-1/20-1/30-1/42
=1/4-1/20-1/30-1/42
=1/5-1/30-1/42
=1/6-1/42
=1/7
希望可以帮到你。
=1/2-(1/6+1/12+1/20+1/30+1/42)
=1/2-(2/12+1/12+1/20+1/30+1/42)
=1/2-(3/12+1/20+1/30+1/42)
=1/2-(1/4+1/20+1/30+1/42)
=1/2-(5/20+1/20+1/30+1/42)
=1/2-(6/20+1/30+1/42)
=1/2-(3/10+1/30+1/42)
=1/2-(9/30+1/30+1/42)
=1/2-(10/30+1/42)
=1/2-(1/3+1/42)=1/2-(14/42+1/42)
=1/2-5/14
=7/14-5/14
=2/14=1/7
关键是通分 这样计算会比较简单
步骤比较多 写的比较详细了 做题的时候没必要这么详细
祝学习进步
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