Toán Lớp 7: tìm x : (1/2 +3x).(x^2 – 4/9) + 0 x^2 là x mũ 2

(1/2 + 3x) . (x^{2} – 4/9) = 0

$\Rightarrow$ $\left[\begin{matrix} \dfrac{1}{2}+3x=0\\ x^2 – \dfrac{4}{9}=0\end{matrix}\right.$

$\Rightarrow$ $\left[\begin{matrix} 3x=0-\dfrac{1}{2}\\ x^2 =0+\dfrac{4}{9}\end{matrix}\right.$

$\Rightarrow$ $\left[\begin{matrix} 3x=\dfrac{-1}{2}\\ x^2 =\dfrac{4}{9}\end{matrix}\right.$

$\Rightarrow$ $\left[\begin{matrix} x=\dfrac{-1}{2}:3\\ x^2 =(\pm\dfrac{2}{3})^2\end{matrix}\right.$

$\Rightarrow$ $\left[\begin{matrix} x=\dfrac{-1}{6}\\ x=\pm\dfrac{2}{3}\end{matrix}\right.$

$\text{Vậy}$ x \in {-1/6 ; 2/3 ; -2/3}