3x3 - 27 x = 0
=> 3x ( x2 - 9 ) = 0
\(=>\orbr{\begin{cases}3x=0\\x^2-9=0\end{cases}}\)
\(=>\orbr{\begin{cases}x=0\\x^2=9\end{cases}}\)
=> x = + 3
hoặc x = 0
\(3x^2-27x=0\)
\(\Leftrightarrow3x\left(x+3\right)\left(x-3\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x=0\\x=\pm3\end{cases}}\)