\(\left(x^2-2x\right)^2-6\left(x^2-2x\right)+8=0\)
\(\Leftrightarrow\left(x^2-2x\right)^2-2\left(x^2-2x\right)-4\left(x^2-2x\right)+8=0\)
\(\Leftrightarrow\left(x^2-2x-2\right)\left(x^2-2x\right)-4\left(x^2-2x-2\right)=0\)
\(\Leftrightarrow\left(x^2-2x-2\right)\left(x^2-2x-4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2-2x-2=0\\x^2-2x-4=0\end{matrix}\right.\) \(\Rightarrow\) casio