由(1-1/2002)+(1-2/2002)+(1-3/2002)+.+(1-2001/2002)
=2001-(1/2002)(1+2+3+.+2001)
=2001-(1/2002)×[(1+2001)×2001÷2]
=2001-2001/2
=2001/2.
由(1-1/2002)+(1-2/2002)+(1-3/2002)+.+(1-2001/2002)
=2001-(1/2002)(1+2+3+.+2001)
=2001-(1/2002)×[(1+2001)×2001÷2]
=2001-2001/2
=2001/2.