1/2-1/6-1/12-1/20-1/30-1/42
=(1-1/2)-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-(1/5-1/6)-(1/6-1/7)
=1-1/2-1/2+1/3-1/3+1/4-1/4+1/5-1/5+1/6-1/6+1/7
=1/7
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1/2-1/6-1/12-1/20-1/30-1/42
=(1-1/2)-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-(1/5-1/6)-(1/6-1/7)
=1-1/2-1/2+1/3-1/3+1/4-1/4+1/5-1/5+1/6-1/6+1/7
=1/7
如果本题有什么不明白可以追问,如果满意请点击右下角“好评”
另外发并点击我的头像向我求助,请谅解,