\(\left(x-1\right)\left(x^2-x+1\right)-2x=x\left(x+1\right)\left(x-1\right)\)
\(\Leftrightarrow\left(x-1\right)\left(x^2-x+1\right)-2x-x\left(x+1\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x^2-x+1-x^2-x\right)-2x=0\)
\(\Leftrightarrow\left(x-1\right)\left(-2x+1\right)-2x=0\)
\(\Leftrightarrow-2x^2+3x-1-2x=0\)
\(\Leftrightarrow-2x^2+x-1=0\)
\(\Leftrightarrow x^2-\dfrac{1}{2}x+\dfrac{1}{2}=0\)
\(\Leftrightarrow x^2-2.\dfrac{1}{4}x+\dfrac{1}{16}+\dfrac{7}{16}=0\)
\(\Leftrightarrow\left(x-\dfrac{1}{4}\right)^2=-\dfrac{7}{16}\) (vô lí)
-Vậy \(S=\)∅
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