so sánh A = 2009 . 2011 và B=\(2010^2\)
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A = \(\dfrac{2008}{2009+2010+2011}+\dfrac{2009}{2009+2010+2011}+\dfrac{2010}{2009+2010+2011}\)
Ta có:
\(\dfrac{2008}{2009}>\dfrac{2008}{2009+2010+2011}\)
\(\dfrac{2009}{2010}>\dfrac{2009}{2009+2010+2011}\)
\(\dfrac{2010}{2011}>\dfrac{2010}{2009+2010+2011}\)
Từ 3 điều trên suy ra : A < B


Ta có :
�=20092010−220092011−2<1B=20092011−220092010−2<1
⇔�<20092010−2+201120092011−2+2011=20092010+200920092011+2009=2009(20092009+1)2009(20092010+1)=20092009+120092010+1=�⇔B<20092011−2+201120092010−2+2011=20092011+200920092010+2009=2009(20092010+1)2009(20092009+1)=20092010+120092009+1=A
⇔�>�⇔A>B

Ta có :
\(B=\dfrac{2009^{2010}-2}{2009^{2011}-2}< 1\)
\(\Leftrightarrow B< \dfrac{2009^{2010}-2+2011}{2009^{2011}-2+2011}=\dfrac{2009^{2010}+2009}{2009^{2011}+2009}=\dfrac{2009\left(2009^{2009}+1\right)}{2009\left(2009^{2010}+1\right)}=\dfrac{2009^{2009}+1}{2009^{2010}+1}=A\)
\(\Leftrightarrow A>B\)



\(A=2009.2011\)
\(B=2010.2010\)
Xét A:
\(2009.2011=2009.\left(2010+1\right)=2009.2010+2009\)
Xét B:
\(2010.2010=2010.\left(2009+1\right)=2010.2009+2010\)
Mà \(2009.2010+2009< 2010.2009+2010\)\(\Rightarrow A< B\)
Vậy A < B
Ta có: \(A=2009.2011=2009\left(2010+1\right)=2009.2010+2009\)
\(B=2010^2=2010.2010=2010\left(2009+1\right)=2009.2010+2010\)
Vì \(2009< 2010\Rightarrow2009.2010+2009< 2009.2010+2010\Rightarrow A< B\)
Vậy A<B