Question

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Answer 1

\(f,\dfrac{x^2}{1+x^4}\le\dfrac{1}{2}\\ \Leftrightarrow2x^2\le1+x^4\\ \Leftrightarrow x^4-2x^2+1\ge0\\ \Leftrightarrow\left(x^2-1\right)^2\ge0\left(luôn.đúng\right)\)

Dấu "=" xảy ra \(\Leftrightarrow x^2-1=0 \Leftrightarrow x^2=1\\ \Leftrightarrow x=\pm1\)