(2/2009+4/2009+6/2009+···+2008/2009)—(1/2009+3/2009+5/2009+···+2007/2009)=[(2+4+6+...+2008)-(1+3+5+...+2007)]/2009=[(2-1)+(4-3)+(6-5)+...+(2008-2007)]/2009=1004/2009