由(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+。。。+(-1/2011×1/2012)
=-[(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+。。。+(1/2011-1/2012)
=-(1/2-1/2012)
=1005/2012.
方法:裂项法,
即1/5×6/1=1/5-1/6.
由(-1×1/2)+(-1/2×1/3)+(-1/3×1/4)+。。。+(-1/2011×1/2012)
=-[(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+。。。+(1/2011-1/2012)
=-(1/2-1/2012)
=1005/2012.
方法:裂项法,
即1/5×6/1=1/5-1/6.