\(\Leftrightarrow\left|7x\right|=3x-1\)
\(\Leftrightarrow\left\{{}\begin{matrix}x>=\dfrac{1}{3}\\\left(7x-3x+1\right)\left(7x+3x-1\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x>=\dfrac{1}{3}\\\left(4x+1\right)\left(10x-1\right)=0\end{matrix}\right.\Leftrightarrow x\in\left\{-\dfrac{1}{4};\dfrac{1}{10}\right\}\)