\(\left(x^2+1\right).\left(x-2\right)-2x=-4\)
\(\left(x^2+1\right).\left(x-2\right)-2x+4=0\)
\(\left(x^2+1\right).\left(x-2\right)-\left(2x-4\right)=0\)
\(\left(x^2+1\right).\left(x-2\right)-2\left(x-2\right)=0\)
\(\left(x-2\right).\left(x^2+1-2\right)=0\)
\(\left(x-2\right).\left(x^2-1\right)=0\)
\(\left(x-2\right).\left(x+1\right).\left(x-1\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=2\\x=-1\\x=1\end{matrix}\right.\)