{Toán 8} Chứng minh bất đẳng thức!

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phamhuy20011801

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Đề
\Leftrightarrow $a^2+b^2+c^2+d^2$ \geq ab+ac+ad
\Leftrightarrow $a^2+b^2+c^2+d^2-ab-ac-ad$ \geq 0
\Leftrightarrow $(\frac{a^2}{4}+b^2-ab)+(\frac{a^2}{4}+c^2-ac)+(\frac{a^2}{4}+d^2-ad)+\frac{a^2}{4}$ \geq 0
\Leftrightarrow $(\frac{a^2}{2}-b)^2+(\frac{a^2}{2}-c)^2+(\frac{a^2}{2}-d)^2+(\frac{a}{2})^2$ \geq 0 (luôn đúng)
 
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