\(x^3=9x\\ =>x^3-9x=0\\ =>x\left(x^2-9\right)=0\\ =>x\left(x-3\right)\left(x+3\right)=0\\ =>\left[{}\begin{matrix}x=0\\x+3=0\\x-3=0\end{matrix}\right.=>\left[{}\begin{matrix}x=0\\x=-3\\x=3\end{matrix}\right.\)
\(\Leftrightarrow x\left(x-3\right) \left(x+3\right)=0\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-3\\x=3\end{matrix}\right.\)
\(x^3=9x\)
\(<=>x^3+9x=0\)
\(<=>x(x^2+9)=0\)
\(<=>x(x^2+3^2)=0\)
\(<=>x(x+3)(x-3)=0\)
\(<=>[x=0<=>[x=0\)
\(<=>[x+3=0<=>[x=-3\)
\(<=>[x-3=0<=>[x=3\)
x 3 - 9x
= x (x2 - 9)
= x (x2 - 32)
= x (x - 3) (x + 3)
