a: \(\Leftrightarrow\left[{}\begin{matrix}3x-1=x-2\left(x>=\dfrac{1}{3}\right)\\3x-1=2-x\left(x< \dfrac{1}{3}\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\left(loại\right)\\x=\dfrac{3}{4}\left(loại\right)\end{matrix}\right.\)