Vì (3x-9)(11-x) = 0 nên ta có (3x-9)=0 hay (11-x) = 0
* 3x-9=0
3x= 0+9
x= 9 : 3
x= 3
* 11-x =0
x= 11-0 = 11
Vậy x = 3 hay x=11
\(\left(3x-9\right)\left(11-x\right)=0\Leftrightarrow\left[{}\begin{matrix}3x-9=0\\11-x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=11\end{matrix}\right.\)