zjy520
幼苗
共回答了15个问题采纳率:93.3% 举报
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)+.+(1/2004-1/2005)]
=2005*[1-1/2005]
=2005*[2004/2005]
=2004
1年前
5