\(\Leftrightarrow x^4-4x^3+4x^2-4x^3+16x^2-16x+3x^2-12x+12\le0\)
\(\Leftrightarrow x^2\left(x^2-4x+4\right)-4x\left(x^2-4x+4\right)+3\left(x^2-4x+4\right)\le0\)
\(\Leftrightarrow\left(x^2-4x+3\right)\left(x-2\right)^2\le0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x^2-4x+3\le0\end{matrix}\right.\) \(\Rightarrow1\le x\le3\)
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