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viet_tranmaininh

Ta có( tìm Min)
[TEX]2x^2 +2y^2\geq 4xy[/TEX]
[TEX]x^2 +4 \geq 4x[/TEX]
[TEX]y^2 +4 \geq 4y[/TEX]
\Rightarrow [TEX]3( x^2 +y^2) \geq 32-8 \Leftrightarrow x^2+y^2 \geq 8[/TEX]
dấu '=' xảy ra \Leftrightarrow [TEX]x =y= 2[/TEX]
 
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