1/(1×2)+1/(2×3)+1/(3×4)+...+1/(2012×2013)
=1-1/2+1/2-1/3+1/3-1/4+...+1/2012-1/2013
=1-1/2013
=2012/2013
1/(1×2)+1/(2×3)+1/(3×4)+...+1/(2012×2013) -1
=1-1/2+1/2-1/3+1/3-1/4+...+1/2012-1/2013-1
=1-1/2013-1
=-1/2013,结果是负值。
1/1×2+1/2×3+1/3×4+…+1/2012×2013 -1
=1-1/2+1/2-1/3+1/3-1/4+……+1/1012-1/2013-1
=﹣1/2013.
简单啊,你通分一下看看呢