\(x\left(x-\dfrac{1}{3}\right)< 0\)
\(\Rightarrow\left\{{}\begin{matrix}x>0\\x-\dfrac{1}{3}< 0\end{matrix}\right.\) hay \(\left\{{}\begin{matrix}x< 0\\x-\dfrac{1}{3}>0\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x>0\\x< \dfrac{1}{3}\end{matrix}\right.\left(chọn\right)\) hay \(\left\{{}\begin{matrix}x< 0\\x>\dfrac{1}{3}\end{matrix}\right.\)
Vậy \(0< x< \dfrac{1}{3}\)
\(x\left(x-\dfrac{1}{3}\right)< 0\)
\(\Rightarrow\left\{{}\begin{matrix}x< 0\\x-\dfrac{1}{3}>0\Rightarrow x>\dfrac{1}{3}\end{matrix}\right.\)
\(\Rightarrow\dfrac{1}{3}< x< 0\Rightarrow x\in\varnothing\)
\(\Rightarrow\left\{{}\begin{matrix}x>0\\x-\dfrac{1}{3}< 0\Rightarrow x< \dfrac{1}{3}\end{matrix}\right.\)
\(\Rightarrow0< x< \dfrac{1}{3}\left(TM\right)\)
\(x\left(x-\dfrac{1}{3}\right)< 0\)
Ta có : \(x>x-\dfrac{1}{3}\)
\(\Rightarrow\left\{{}\begin{matrix}x>0\\x-\dfrac{1}{3}< 0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x>0\\x< \dfrac{1}{3}\end{matrix}\right.\Rightarrow0< x< \dfrac{1}{3}\)
Vậy \(0< x< \dfrac{1}{3}\)
Em làm vậy có dài lắm không Nguyễn Huy Tú 
