Question

Tìm x \(\in\) Q, biết (x+3)(2x-4)<0

Answer 1

\((x+3)(2x-4)<0\\\Leftrightarrow 2(x+3)(x-2)<0\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x+3>0\\x-2< 0\end{matrix}\right.\\\left\{{}\begin{matrix}x+3< 0\\x-2>0\end{matrix}\right.\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>-3\\x< 2\end{matrix}\right.\\\left\{{}\begin{matrix}x< -3\\x>2\end{matrix}\right.\left(vô.lí\right)\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x>-3\\x< 2\end{matrix}\right.\)

\(\Leftrightarrow-3< x< 2\)

#\(Toru\)