-1/n × 1/(n + 1) = -1/n + 1/(n + 1)
(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2006×1/2007)
=(-1 + 1/2)+(-1/2 + 1/3)+(-1/3 + 1/4) + …+(
-1/2006 + 1/2007)
= -1 + 1/2 -1/2 + 1/3 -1/3 + 1/4 - …-1/2006 + 1/2007
= -1 + 1/2007
= -2006/2007
-1/n × 1/(n + 1) = -1/n + 1/(n + 1)
(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+…+(-1/2006×1/2007)
=(-1 + 1/2)+(-1/2 + 1/3)+(-1/3 + 1/4) + …+(
-1/2006 + 1/2007)
= -1 + 1/2 -1/2 + 1/3 -1/3 + 1/4 - …-1/2006 + 1/2007
= -1 + 1/2007
= -2006/2007