Tìm GTNN và GTLN hay

E

eye_smile

$xy(2013-\dfrac{xy}{2})=\dfrac{x^4}{4}+\dfrac{y^4}{4}-2014 \ge \dfrac{(x^2+y^2)^2}{8}-2014 \ge \dfrac{x^2y^2}{2}-2014$

\Rightarrow $(xy)^2 -2013xy-2014 \le 0$

\Leftrightarrow $-1 \le xy \le 2014$
 
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