1986*1987/1+1987*1988/1+1988*1989+……+2001*2002/1+2002/1
= 1986*1987/1+1987*1988/1+1988*1989+……+(2001*2002/1+2001*2002/2001)
= 1986*1987/1+1987*1988/1+1988*1989+……+2001*2002/(1+2001)
= 1986*1987/1+1987*1988/1+1988*1989+……+2001/1
(由此类推)
=1986/1
1986*1987/1+1987*1988/1+1988*1989+……+2001*2002/1+2002/1
=1/1986-1/1987+1/1987-1/1988+...+1/2001-1/2002+1/2002
=1/1986
1/(1986×1987)+1/(1987×1988)+1/(1988×1989)+……1/(2001×2002)+1/2002
=1/1986-1/1987+1/1987-1/1988+1/1988-1/1989+……+1/2001-1/2002+1/2002
=1/1986