Toan 9

E

eye_smile

$A=\dfrac{2(x+2)^2}{3(x+2)^2}+\dfrac{(x-1)^2}{3(x+2)^2}=\dfrac{2}{3}+\dfrac{(x-1)^2}{3(x+2)^2} \ge \dfrac{2}{3}$

Dấu "=" xảy ra \Leftrightarrow $x=1$
 
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