│1/3-1/2│+│1/4-1/3│+│1/5-1/4│+│1/6-1/5│+........+│1/2012-1/2011│=1/2-1/3+1/3-1/4+1/4-1/5+........+1/2011-1/2012=1/2-1/2012=1005/2012
