\(C=\dfrac{\left(2-x\right)^3}{x^2\left(x-2\right)+x-2}=\dfrac{\left(2-x\right)^3}{\left(x^2+1\right)\left(x-2\right)}=-\dfrac{\left(2-x\right)^3}{\left(x^2+1\right)\left(x-2\right)}=-\dfrac{\left(2-x\right)^2}{x^2+1}\)
Do \(\left\{{}\begin{matrix}\left(2-x\right)^2\ge0\\x^2+1\ge1\end{matrix}\right.\) ;\(\forall x\)
\(\Rightarrow\dfrac{\left(2-x\right)^2}{x^2+1}\ge0;\forall x\)
\(\Rightarrow-\dfrac{\left(2-x\right)^2}{x^2+1}\le0;\forall x\)
Vậy đa thức C không dương
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