13 ) 3x² - 9x = 0
⇔ 3x ( x - 3 ) = 0
⇔$\left[\begin{matrix} 3x=0\\ x-3=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=3\end{matrix}\right.$
Vậy x = 0 hoặc x = 3
14 ) 5x² - 10x = 0
⇔ 5x ( x - 2 ) = 0
⇔ $\left[\begin{matrix} 5x=0\\ x-2=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=2\end{matrix}\right.$
Vậy x = 0 hoặc x = 2
15 ) 6x² - 24x = 0
⇔ 6x ( x - 4 ) =0
⇔$\left[\begin{matrix} 6x=0\\ x- 4=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=4\end{matrix}\right.$
Vậy x = 0 hoặc x = 4
16 ) 3x² - 12x = 0
⇔ 3x ( x - 4 ) = 0
⇔$\left[\begin{matrix} 3x=0\\ x- 4=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=4\end{matrix}\right.$
Vậy x = 0 hoặc x = 4
17 ) 5x² + 20x = 0
⇔ 5x ( x + 4 ) = 0
⇔$\left[\begin{matrix} 5x=0\\ x+ 4=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=-4\end{matrix}\right.$
Vậy x = 0 hoặc x = -4
18 ) 6x² + 18x = 0
⇔ 6x ( x + 3 ) =0
⇔$\left[\begin{matrix} 6x=0\\ x+ 3=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=-3\end{matrix}\right.$
Vậy x = 0 hoặc x = -3
19 ) 3x³ + 9x² = 0
⇔ 3x² ( x + 3 ) = 0
⇔$\left[\begin{matrix} 3x²=0\\ x+ 3=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=-3\end{matrix}\right.$
Vậy x = 0 hoặc x = -3
20 ) 5x³ + 25x² = 0
⇔ 5x² ( x + 5 ) = 0
⇔$\left[\begin{matrix} 5x²=0\\ x+ 5=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=-5\end{matrix}\right.$
Vậy x = 0 hoặc x = -5
21) 6x³ + 12x² = 0
⇔ 6x² ( x + 2 ) = 0
⇔$\left[\begin{matrix} 6x²=0\\ x+ 2=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=-2\end{matrix}\right.$
Vậy x = 0 hoặc x = -2
22) 6x² - 4x = 0
⇔ 2x ( 3x - 2 ) =0
⇔$\left[\begin{matrix} 2x=0\\ 3x- 2=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ 3x=2\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=2/3\end{matrix}\right.$
Vậy x = 0 hoặc x = 2/3
23) 9x² - 12x = 0
⇔ 3x ( 3x - 4 ) =0
⇔$\left[\begin{matrix} 3x=0\\ 3x- 4=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ 3x=4\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=4/3\end{matrix}\right.$
Vậy x = 0 hoặc x = 4/3
24) 4x² - 10x = 0
⇔ 2x ( 2x - 5 ) =0
⇔$\left[\begin{matrix} 2x=0\\ 2x- 5=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ 2x=5\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=5/2\end{matrix}\right.$
Vậy x = 0 hoặc x = 5/2
25 ) 6x - 4x² = 0
⇔ 2x ( 3 - 2x ) = 0
⇔$\left[\begin{matrix} 2x=0\\ 3- 2x=0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ 2x=3\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=3/2\end{matrix}\right.$
Vậy x = 0 hoặc x = 3/2
26 ) 4x - 3x² = 0
⇔ x ( 4 - 3x ) = 0
⇔$\left[\begin{matrix} x=0\\ 4- 3x =0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ 3x=4\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=4/3\end{matrix}\right.$
Vậy x = 0 hoặc x = 4/3
27 ) 5x - 7x² = 0
⇔ x ( 5 - 7x ) = 0
⇔$\left[\begin{matrix} x=0\\ 5- 7x =0\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ 7x=5\end{matrix}\right.$
⇔$\left[\begin{matrix} x=0\\ x=5/7\end{matrix}\right.$
Vậy x = 0 hoặc x = 5/7
