5x.(9-x) - 15.(9-x)= 0
(9-x).(5x-15) = 0
=> 9-x = 0 => x = 9
5x -15 = 0 => 5x = 15 => x = 3
KL:...
\(\left(9-x\right)\left(5x-15\right)=0\)
\(\Leftrightarrow5\left(9-x\right)\left(x-3\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-9=0\\x-3=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=9\\x=3\end{cases}}}\)
5x(9-x)-15(9-x)=0
(9-x).(5-15)=0
(9-x).(-10)=0
-90-(-10x)=0
-90+10x=0
10x=0+90=90
x=90:10
Vậy x= 9
5x (9 - x) - 15 (9 - x) = 0
(9 - x) (5x - 15) = 0
(9 - x) 5(x - 3) = 0
9 - x = 0 hay x - 3 = 0
x = 9 hay x = 3
