\(\Leftrightarrow x^4-\left(x^2-2x+1\right)< 0\)
\(\Leftrightarrow x^4-\left(x-1\right)^2< 0\)
\(\Leftrightarrow\left(x^2-x+1\right)\left(x^2+x-1\right)< 0\)
\(\Leftrightarrow x^2+x-1< 0\) (do \(x^2-x+1=\left(x-\frac{1}{2}\right)^2+\frac{3}{4}>0\) \(\forall x\))
\(\Rightarrow\frac{-1-\sqrt{5}}{2}< x< \frac{-1+\sqrt{5}}{2}\)