1/1*2+1/2*3+1/3*4.+1/2011*2012+1/2012*2013
问题描述：
1/1*2+1/2*3+1/3*4.+1/2011*2012+1/2012*2013
答
1/1*2+1/2*3+1/3*4.+1/2011*2012+1/2012*2013
=1-1/2+1/2-1/3+1/3-1/4+...+1/2011-1/2012+1/2012-1/2013
=1-1/2013
=2012/2013