1/1*3+1/3*5+1/5*7+.......+1/2011*2013
=(1-1/3)+(1/3-1/5)+(1/5-1/7)+......+(1/2011-1/2013)
=1-1/3+1/3-1/5+1/5-1/7+.....+1/2011-1/2013
=1-1/2013
=2012/2013
=(1-1/3)+(1/3-1/5)+(1/5-1/7)+......+(1/2011-1/2013)
=1-1/3+1/3-1/5+1/5-1/7+.....+1/2011-1/2013
=1-1/2013
=2012/2013