So Sánh
\(\frac{2007}{2008}+\frac{2008}{2009}\)và \(\frac{2007}{2008}+\frac{2008}{2009}\)
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ta có: \(A=\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2009}+\frac{2009}{2006}\)
A = \(1-\frac{1}{2007}+1-\frac{1}{2008}+1-\frac{1}{2009}+1+\frac{3}{2006}\)
A= \(4\)\(+\frac{3}{2006}-\left(\frac{1}{2007}+\frac{1}{2008}+\frac{1}{2009}\right)\)
Do 1/2007 < 1/2006 ; 1/2008<1/2006 ; 1/2009<1/2006=> 1/2007 + 1/2008 + 1/2009 < 1/2006 + 1/2006 + 1/2006
Mà 1/2006 + 1/2006 + 1/2006 = 3/2006
=> 3/2006 -( 1/2007 + 1/2008 + 1/2009) > 0
=> \(4+\frac{3}{2006}-\left(\frac{1}{2007}+\frac{1}{2008}+\frac{1}{2009}\right)>4\)
=> A > 4
Ta có:\(\frac{2006}{2007}< 1\)
\(\frac{2007}{2008}< 1\)
\(\frac{2008}{2009}< 1\)
\(\frac{2009}{2006}>1\)\(\frac{2006}{2007}+\frac{2007}{2008}+\frac{2008}{2009}+\frac{2009}{2006}< 4\)
Ta có:4=1+1+1+1=\(\frac{2009}{2009}+\frac{2010}{2010}+\frac{2011}{2011}+\frac{2008}{2008}\)
\(\frac{2008}{2009}+\frac{1}{2009}+\frac{2009}{2010}+\frac{1}{2010}+\frac{2010}{2011}+\frac{1}{2011}+\frac{2008}{2008}\)
Xét \(A=\frac{2008}{2009}+\frac{2009}{2010}+\frac{2010}{2011}+\frac{2011}{2008}\)
\(=\frac{2009}{2009}+\frac{2010}{2010}+\frac{2011}{2011}+\frac{2008}{2008}+\frac{1}{2008}+\frac{1}{2008}+\frac{1}{2008}\)
xét \(\frac{1}{2009}< \frac{1}{2008};\frac{1}{2010}< \frac{1}{2008};\frac{1}{2011}< \frac{1}{2008}\)
\(\Rightarrow4< A\)
A=\(\frac{2007^{2007}}{2008^{2008}}\)
B=\(\frac{2008^{2008}}{2009^{2009}}\)
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 ...
\(\frac{2007}{2008}\)\(+\)\(\frac{2008}{2009}\)\(=\)\(\frac{2007}{2008}\)\(+\)\(\frac{2008}{2009}\)
k mk nha!!! *o~
\(\frac{2007}{2008}+\frac{2008}{2009}=\frac{2007}{2008}+\frac{2008}{2009}\)
nha ^_^
Nguyễn Vân Anh