Đáp án+Giải thích các bước giải:
`A=2006/2007+2007/2008+2008/2009+2009/2006`
`=(2007-1)/2007+(2008-1)/2008+(2009-1)/2009+(2006+3)/2006`
`=1-1/2007+1-1/2008+1-1/2009+1+3/2006`
`=4+3/2006-1/2007-1/2008-1/2009`
`=4+1/2006+1/2006+1/2006-1/2007-1/2008-1/2009`
Vì `1/2006>1/2007`
`1/2006>1/2008`
`1/2006>1/2009`
`=>1/2006+1/2006+1/2006-1/2007-1/2008-1/2009>0`
`=>4+1/2006+1/2006+1/2006-1/2007-1/2008-1/2009>4`
Hay `A>B.`