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|1/2 -1|+|1/3-1/2|+|1/4-1/3|+.+|1/2009-1/2008| =1-1/2+1/2-1/3+1/3-1/4+.1/2008-1/2009 =1-1/2009 =2008/2009 每個絕對值裏的數都小於零,去掉絕對值時變號 不懂得繼續問哦^_^
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