
急~~~帮帮忙啊
1个回答
展开全部
(1-3/2)+(5/6-7/12)+(9/20-11/30)+(13/42-15/56)+(17/72-19/90)+21/110
=(-1/2+1/4+1/12+1/24+1/40)+21/110
=-1/10+21/110
=-1/11
=(-1/2+1/4+1/12+1/24+1/40)+21/110
=-1/10+21/110
=-1/11
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