\(x^4-9x^3+24x^2-27x+9=0\)
<=> \(x^4-3x^3+3x^2-6x^3+18x^2-18x+3x^2-9x+9=0\)
<=>\(x^2\left(x^2-3x+3\right)-6x\left(x^2-3x+3\right)+3\left(x^2-3x+3\right)=0\)
<=>\(\left(x^2-6x+3\right)\left(x^2-3x+3\right)=0\)
<=> \(\left[{}\begin{matrix}x^2-6x+3=0\\x^2-3x+3=0\end{matrix}\right.\)
Giải nốt :))