$\text{~~Holi~~}$
$\text{_Bài làm_}$
$\text{Sửa đề chút nha.}$
$a. 5x(x-2)+3x-6=0$
$⇔ 5x(x-2)+(3x-6)=0$
$⇔ 5x(x-2)+3(x-2)=0$
$⇔ (x-2)(5x+3)=0$
$⇒ \left[ \begin{array}{l}x-2=0\\5x+3=0\end{array} \right. $
$⇔ \left[ \begin{array}{l}x=2\\x=\frac{-3}{5} \end{array} \right.$
$\text{Vậy x=2, x=$\frac{-3}{5}$ }$
$b. x³-9x=0$
$⇔ x(x²-9)=0$
$⇔ \left[ \begin{array}{l}x=0\\x^2-9=0\end{array} \right.$
$⇔ \left[ \begin{array}{l}x=0\\x=±9\end{array} \right.$
$\text{Vậy x=0, x=±9} $
$c. 3x³-9x=0$
$⇔ 3x(x²-3)=0$
$⇔ \left[ \begin{array}{l}3x=0\\x^2-3=0\end{array} \right. $
$⇔ \left[ \begin{array}{l}x=0\\x^2=±3\end{array} \right.$
$\text{Vậy x=0, x=±3}$
$d. 7x²-28=0$
$⇔ 7x²=28$
$⇔ x²=4$
$⇔ x=±4$
$\text{Vậy x=±4}$
$e. x²-2x-15=0$
$⇔ x²-5x+3x-15=0$
$⇔ (x²-5x)+(3x-15)=0$
$⇔ x(x-5)+3(x-5)=0$
$⇔ (x-5)(x+3)=0$
$⇒ \left[ \begin{array}{l}x-5=0\\x+3=0\end{array} \right.$
$⇔ \left[ \begin{array}{l}x=5\\x=-3\end{array} \right.$
$\text{Vậy x=5, x=-3}$
