Question

计算1/1x4+1/4x7+1/7x10+.+1/2002x2005+1/2005x2008

Answer 1

＝3(1/1-1/4)+3(1/4-1/7)＋……＋3(1/2002-1/2005)＋3(1/2005-1/2008)

＝3(1/1-1/4+1/4-1/7+……＋1/2002=1/2005+1/2005-1/2008)

＝3(1-1/2008)=3*(2007/2008)