Môn Toán Lớp 7: (X+3/4).(x-1/3)>0 b, (x-2).(x+2/3)>0

$\text{a) (x + $\dfrac{3}{4}$)(x – $\dfrac{1}{3}$) > 0}$

$\text{⇔ $\left[\begin{matrix} \begin{cases} x + \dfrac{3}{4} > 0\\x – \dfrac{1}{3} > 0 \end{cases}\\ \begin{cases} x + \dfrac{3}{4} < 0\\x – \dfrac{1}{3} < 0 \end{cases}\end{matrix}\right.$}$

$\text{⇔ $\left[\begin{matrix} \begin{cases} x > -\dfrac{3}{4}\\x > \dfrac{1}{3} \end{cases}\\ \begin{cases} x < -\dfrac{3}{4}\\x < \dfrac{1}{3} \end{cases}\end{matrix}\right.$}$

$\text{⇔ $\left[\begin{matrix} x > \dfrac{1}{3}\\ x < -\dfrac{3}{4}\end{matrix}\right.$}$

$\text{Vậy x > $\dfrac{1}{3}$ hoặc x < -$\dfrac{3}{4}$}$

$\text{b) (x – 2)(x + $\dfrac{2}{3}$) > 0}$

$\text{⇔ $\left[\begin{matrix} \begin{cases} x – 2 > 0\\x + \dfrac{2}{3} > 0 \end{cases}\\ \begin{cases} x – 2 < 0\\x + \dfrac{2}{3} < 0 \end{cases}\end{matrix}\right.$}$

$\text{⇔ $\left[\begin{matrix} \begin{cases} x > 2\\x > -\dfrac{2}{3} \end{cases}\\ \begin{cases} x < 2\\x < -\dfrac{2}{3} \end{cases}\end{matrix}\right.$}$

$\text{⇔ $\left[\begin{matrix} x > 2\\ x < -\dfrac{2}{3}\end{matrix}\right.$}$

$\text{Vậy x > 2 hoặc x < -$\dfrac{2}{3}$}$

$\textit{Ha1zzz}$