(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2008×1/2009)

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(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2008×1/2009)

(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2008×1/2009)
(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2008×1/2009)

(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2008×1/2009)
(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2008×1/2009)
=1/2-1+1/3-1/2+1/4-1/3+…+1/2009-1/2008
=-1+1/2009
=-2008/2009