a) Ta có: \(\left(x-\frac{1}{5}\right).\left(x+\frac{4}{7}\right)>0\)
+ \(\hept{\begin{cases}x-\frac{1}{5}>0\\x+\frac{4}{7}>0\end{cases}}\)\(\Leftrightarrow\)\(\hept{\begin{cases}x>\frac{1}{5}\\x>-\frac{4}{7}\end{cases}}\)\(\Rightarrow\)\(x>\frac{1}{5}\)
+ \(\hept{\begin{cases}x-\frac{1}{5}< 0\\x+\frac{4}{7}< 0\end{cases}}\)\(\Leftrightarrow\)\(\hept{\begin{cases}x< \frac{1}{5}\\x< -\frac{4}{7}\end{cases}}\)\(\Rightarrow\)\(x< -\frac{4}{7}\)
Vậy \(x>\frac{1}{5}\)hoặc \(x< -\frac{4}{7}\)
b) Ta có: \(\left(x+\frac{2}{3}\right).\left(x+2\right)< 0\)
+ \(\hept{\begin{cases}x+\frac{2}{3}>0\\x+2< 0\end{cases}}\)\(\Leftrightarrow\)\(\hept{\begin{cases}x>-\frac{2}{3}\\x< -2\end{cases}}\)\(\Rightarrow\)\(-\frac{2}{3}< x< -2\)( vô lí )
+ \(\hept{\begin{cases}x+\frac{2}{3}< 0\\x+2>0\end{cases}}\)\(\Leftrightarrow\)\(\hept{\begin{cases}x< -\frac{2}{3}\\x>-2\end{cases}}\)\(\Rightarrow\)\(-\frac{2}{3}>x>-2\)
Vậy \(-2< x< -\frac{2}{3}\)
a) Xét hai trường hợp :
1. \(\hept{\begin{cases}x-\frac{1}{5}>0\\x+\frac{4}{7}>0\end{cases}}\Leftrightarrow\hept{\begin{cases}x>\frac{1}{5}\\x>-\frac{4}{7}\end{cases}}\Leftrightarrow x>\frac{1}{5}\)
2. \(\hept{\begin{cases}x-\frac{1}{5}< 0\\x+\frac{4}{7}< 0\end{cases}}\Leftrightarrow\hept{\begin{cases}x< \frac{1}{5}\\x< -\frac{4}{7}\end{cases}}\Leftrightarrow x< -\frac{4}{7}\)
Vậy \(\orbr{\begin{cases}x>\frac{1}{5}\\x< -\frac{4}{7}\end{cases}}\)
b) Xét hai trường hợp :
1. \(\hept{\begin{cases}x+\frac{2}{3}>0\\x+2< 0\end{cases}}\Leftrightarrow\hept{\begin{cases}x>-\frac{2}{3}\\x< -2\end{cases}}\)( loại )
2. \(\hept{\begin{cases}x+\frac{2}{3}< 0\\x+2>0\end{cases}}\Leftrightarrow\hept{\begin{cases}x< -\frac{2}{3}\\x>-2\end{cases}}\Leftrightarrow-2< x< -\frac{2}{3}\)
Vậy -2 < x < -2/3