1/(1*2)+1/(2*3)+1/(3*4)+........+1/(2013*2014)=(1-1/2)+(1/2-1/3)+(1/3-1/4)+........+(1/2013-1/2014)=1-1/2014=2013/2014
=1/2 * 2/3 *3/4*******2013*2014= 1/2014 前面的都约去了
