Ta có : \(A=\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2009}+\frac{2009}{2006}\)

                \(=\frac{2007-1}{2007}+\frac{2008-1}{2008}+\frac{2009-1}{2009}+\frac{2006+3}{2006}\)

                  \(=1-\frac{1}{2007}+1-\frac{1}{2008}+1-\frac{1}{2009}+1+\frac{3}{2006}\)

                  \(=\left(1+1+1+1\right)-\left(\frac{1}{2007}+\frac{1}{2008}+\frac{1}{2009}-\frac{3}{2006}\right)\)

                  \(< 4-\left(\frac{1}{2009}+\frac{1}{2009}+\frac{1}{2009}-\frac{3}{2009}\right)\)     

                    \(=4\)

=> A < 4 

Vậy A < 4 

tôi thích hoa hồng sai kìa

Vì 2006/2007 ; 2007/2008 ; 2008/2009 ; 2009/2010 đều bé hơn 1 nên:

2006/2007 + 2007/2008 + 2008/2009 + 2009/2010 < 1 + 1 + 1 + 1 = 4.

Vậy ...

A=\(\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2009}+\frac{2009}{2006}\)=3-(\(\frac{1}{2007}+\frac{1}{2008}+\frac{1}{2009}\))+1+\(\frac{3}{2006}\)=4+(\(\frac{1}{2006}-\frac{1}{2007}\))+(\(\frac{1}{2006}-\frac{1}{2008}+\frac{1}{2009}\))

=> A>4 (\(\frac{1}{2006}>\frac{1}{2007}>\frac{1}{2008}>\frac{1}{2009}\))

\(A=\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2006}\)

\(A=1-\frac{1}{2007}+1-\frac{1}{2008}+1-\frac{2}{2006}\)

\(A=\left(1+1+1\right)+\left(\frac{1}{2006}-\frac{1}{2007}\right)+\left(\frac{1}{2006}-\frac{1}{2008}\right)\)

\(A=3+\left(\frac{1}{2006}-\frac{1}{2007}\right)+\left(\frac{1}{2006}-\frac{1}{2008}\right)\)

Ta thấy : \(\frac{1}{2006}-\frac{1}{2007}>0\); \(\frac{1}{2006}-\frac{1}{2008}>0\)\(\Rightarrow A>3\)

\(A=\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2006}=1-\frac{1}{2007}+1-\frac{1}{2008}+1+\frac{2}{2006}=3+\left(\frac{1}{2006}-\frac{1}{2007}\right)+\left(\frac{1}{2006}-\frac{1}{2008}\right)\)

Vì 2006<2007, 2006<2008 nên \(\frac{1}{2006}>\frac{1}{2007};\frac{1}{2006}>\frac{1}{2008}=>\frac{1}{2006}-\frac{1}{2007}>0,\frac{1}{2006}-\frac{1}{2008}>0\)

=> \(A=3+\left(\frac{1}{2006}-\frac{1}{2007}\right)+\left(\frac{1}{2006}-\frac{1}{2008}\right)>3=>A>3\)

bạn ơi cái dấu bằng to và dấu lớn to là dấu suy ra ak

\(\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2006}\)

\(\Rightarrow\frac{2008}{2006}>1\)

\(\frac{2006}{2007}< 1;\frac{2007}{2008}< 1\)

\(\Rightarrow\frac{2006}{2007}+\frac{2007}{2008}< 2\)

\(\Rightarrow\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2006}< 3\)

 A =2006/2007+2007/2008+2008/2006

    = \(\frac{2006}{2007}\)+ \(\frac{2007+1}{2008}\)+ \(\frac{2008}{2006+2}\)

    = 1 - \(\frac{1}{2007}\)+ 1 - \(\frac{1}{2008}\)+ 1 + \(\frac{1}{2006}\)+ \(\frac{1}{2006}\)

    = 3 + ( \(\frac{1}{2006}\)- \(\frac{1}{2007}\)) + ( \(\frac{1}{2006}\)- \(\frac{1}{2008}\))

    vì \(\frac{1}{2006}\)> \(\frac{1}{2007}\), \(\frac{1}{2006}\)> \(\frac{1}{2008}\)nên A > 3

Mình nhé bạn :  

http://olm.vn/thanhvien/ngathongminh

2.006/2.007 + 2.007/2.008 < 2006 + 2.007/2.007 + 2.008

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