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.啥意思说下