`(2007+2008)/(2008+2009)` và `2007/2008 + 2008/2009`
`(2007+2008)/(2008+2009)=4015/4017=1-2/4017`(là phân số đã rõ)
`2007/2008 + 2008/2009=(1+1)-1/2008+1/2009=2-1/2008+1/2009`
Ta có:
`⇔1<2` hay `2-1/2008+1/2009<1-2/4017`
`(2007+2008)/(2008+2009) > 2007/2008 + 2008/2009`