1分之1x3+1分之3x5+1分之5x7+.+1分之2011x2013
=1/(1*3)+1/(3*5)+1/(5*7)+……+1/(2011*2013)
=1/2*(1-1/3+1/3-1/5+1/5-1/7+……+1/2011-1/2013)
=1/2*(1-1/2013)
=1/2*2012/2013
=1006/2013 .