3/2>4/3
5/4>6/5
.
2005/2004>2006/2005
(3/2)*(5/4)*.(2005/2004)>(4/3)*(6/5)*.(2006/2005)
[(3/2)*(5/4)*.(2005/2004)]^2>(3/2)*(5/4)*.(2005/2004)*(4/3)*(6/5)*.(2006/2005)=3/2*4/3*5/4*6/5*...*2005/2004*2006/2005=2006/2=1003
即A^2>1003,所以A>根号下1003>31
同理A^2<2005/1=2005,所以A<根号下2005<45