2011X（1-1/2）X(1-1/3)X(1-1/4)X(1-1/5)X.X(1-1/2011)X(1-1/2011)
=2011(1/2)x(2/3)x(3/4)x(4/5)x(5/6)...x(2009/2010)x(2010/2011）(中间项的分子分母可以约掉)
=2011X1/2011
=1
打字累,