a) `x^3-x=0`
`⇒x(x^2-1)=0`
`⇒x(x-1)(x+1)=0`
\(\left[ \begin{array}{l}x=0\\x-1=0\\x+1=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=0\\x=1\\x=-1\end{array} \right.\)
Vậy `x=0; ±1`
b) `x^3-2x^2-9x+18=0`
`⇒(x^3-2x^2)-(9x-18)=0`
`⇒x^2(x-2)-9(x-2)=0`
`⇒(x^2-9)(x-2)=0`
`⇒(x-3)(x+3)(x-2)=0`
\(\left[ \begin{array}{l}x-3=0\\x-2=0\\x+3=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=3\\x=2\\x=-3\end{array} \right.\)
Vậy `x=2; ±3`
c) `(x^2+4)^2-16x^2=0`
`⇒(x^2-4x+4)(x^2+4x+4)=0`
`⇒(x-2)^2(x+2)^2=0`
\(\left[ \begin{array}{l}x-2=0\\x+2=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=2\\x=-2\end{array} \right.\)
Vậy `x=±2`
