用规律计算(-1x1/2)+(-1/2x1/3)+(-1/2011x1/2012)
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用规律计算(-1x1/2)+(-1/2x1/3)+(-1/2011x1/2012)
用规律计算(-1x1/2)+(-1/2x1/3)+(-1/2011x1/2012)
用规律计算(-1x1/2)+(-1/2x1/3)+(-1/2011x1/2012)
-1*1/2+(-1/2*1/3)+.+(-1/2011*1/2012)
=-1+1/2-1/2+1/3+.-1/2011+1/2012
=-1+1/2012
=-2011/2012
-(1x1/2+1/2x1/3+......+1/2011x1/2012)
=-[1-1/2+1/2-1/3......+1/2011-1/2012]
=-[1-1/2012]
=-2011/2012