|1／2－1|＋|1／3－1／2|＋|1／4－1／3|＋...＋|1／2012－1／2011|＋|1／2013－2012|
=1-1/2+1/2-1/3+1/3-1/4+……+1/2011-1/2012+1/2012-1/2013
=1-1/2013
=2012/2013