1x2分之2005 + 2x3分之2005 + 3x4分之2005 + 4x5分之2005······2004X2005分之2005 =2005*[1/(1x2)+1/(2x3)+1/(3x4)+1/(4x5)······1/(2004X2005)]=2005*[(1/1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+.+(1/2...