1\2-1\6-1\12-1\20-1\30-1\42……-1\132
急用帮帮忙呀
人气：365 ℃ 时间：2019-12-26 15:20:29
解答
可化为
1/(1x2)-1/(2x3)-1/(3x4)...-1/(11x12)
=1/2-(1/2-1/3)-(1/3-1/4)-...-(1/11-1/12)
=1/2-1/2+1/3-1/3+1/4-...-1/11+1/12
=1/12
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