1\2,1\3,1\4,1\5,.1\90.1\91中挑出10个数,加上正负号,使它们的和为-1
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![1\2,1\3,1\4,1\5,.1\90.1\91中挑出10个数,加上正负号,使它们的和为-1](/uploads/image/z/2011970-2-0.jpg?t=1%5C2%2C1%5C3%2C1%5C4%2C1%5C5%2C.1%5C90.1%5C91%E4%B8%AD%E6%8C%91%E5%87%BA10%E4%B8%AA%E6%95%B0%2C%E5%8A%A0%E4%B8%8A%E6%AD%A3%E8%B4%9F%E5%8F%B7%2C%E4%BD%BF%E5%AE%83%E4%BB%AC%E7%9A%84%E5%92%8C%E4%B8%BA-1)
1\2,1\3,1\4,1\5,.1\90.1\91中挑出10个数,加上正负号,使它们的和为-1
1\2,1\3,1\4,1\5,.1\90.1\91中挑出10个数,加上正负号,使它们的和为-1
1\2,1\3,1\4,1\5,.1\90.1\91中挑出10个数,加上正负号,使它们的和为-1
-1=-1/5-1/6-1/8-1/9-1/10-1/12-1/15-1/18-1/20-1/24
1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10=1-1/10
所以:
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/10=1
即:
-1/2-1/6-1/12-1/20-1/30-1/42-1/56-1/72-1/90-1/10=-1