2009除以2009又2010分之2009加2011分之一
2009 / (2009+2009/2010) + 1/2011
= 2009 / [ 2009×(1+1/2010) ] + 1/2011
= 1 / (1+1/2010) ] + 1/2011
= 1 / (2011/2010) + 1/2011
= 2010 / 2011 + 1/2011
= 1