2007÷2007又2007/2008-1/2009
=2007÷[(2007×2008+2007)/2008]-1/2009
=2007÷[2007×(2008+1)/2008]-1/2009
=2007÷(2007×2009/2008)-1/2009
=2007×2008/(2007×2009)-1/2009
=2008/2009-1/2009
=2007/2009