a＊b=(a-b)/ab 2＊1+3＊2+4＊3+``````+2009＊2008 =(2-1)/1*2+(3-2)/2*3+(4-3)/3*4+.+(2009-2008)/2008*2009 =1/2+1/6+1/12+.+1/2008*2009 =1-1/2+1/2-1/3+1/3-1/4+.+1/2008-1/2009 =1-1/2009 =2008/2009