a.\(\left|x-3\right|=4x+1\)
\(ĐK:4x+1\ge0\Leftrightarrow4x\ge-1\Leftrightarrow x\ge\dfrac{-1}{4}\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=4x+1\\x-3=-4x-1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x-4x=1+3\\x+4x=-1+3\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}-3x=4\\5x=2\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-4}{3}\left(ktm\right)\\x=\dfrac{2}{5}\left(tm\right)\end{matrix}\right.\)
Vay S \(=\left\{\dfrac{2}{5}\right\}\)
b. \(\left|x-2\right|+2x=10\\ \Leftrightarrow\left|x-2\right|=10-2x\)
ĐK : \(10-2x\ge0\Leftrightarrow-2x\ge-10\Leftrightarrow x\le5\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2=10-2x\\x-2=2x-10\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x+2x=10+2\\x-2x=-10+2\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}3x=12\\-x=-8\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=4\left(tm\right)\\x=8\left(ktm\right)\end{matrix}\right.\)
Vay S \(=\left\{4\right\}\)