Bài 1
`( 1 + 1/2006 ) × ( 1 + 1/2007 ) × ( 1 + 1/2008 ) × ( 1 + 1/2009 )`
`= 2007/2006 × 2008/2007 × 2009/2008 × 2010/1009`
`= {2007 × 2008 × 2009 × 2010}/{2006 × 2007 × 2008 × 2009}`
`= 2010/2006`
Bài 2
`{1999 × 2001 - 1}/{1998 + 1999 × 2000} × 7/5`
`= {1999 × ( 2000 + 1 ) - 1}/{1998 + 1999 × 2000} × 7/5`
`= {1999 × 2000 + 1999 - 1}/{1998 + 1999 × 2000} × 7/5`
`= {1999 × 2000 + 1998}/{1998 + 1999 × 2000} × 7/5`
`= 1 × 7/5`
`= 7/5`
`#dtkc`