\(4-x\left(x-1\right)+x^2=3x\)
\(\Leftrightarrow4-x^2+x+x^2=3x\)
\(\Leftrightarrow-3x+x=-4\)
\(\Leftrightarrow-2x=-4\)
\(\Leftrightarrow x=2\) . Vậy \(S=\left\{2\right\}\)
\(3-\left(4+x\right)x+x^2-1=0\)
\(\Leftrightarrow3-4x-x^2+x^2-1=0\)
\(\Leftrightarrow-4x=-3+1=-2\)
\(\Leftrightarrow x=\dfrac{1}{2}\) . Vậy \(S=\left\{\dfrac{1}{2}\right\}\)