a.\(|3x|=x+7\)
Nếu \(3x\ge0\Leftrightarrow x\ge0\).Khi đó ta có:
\(3x=x+7\)
\(\Leftrightarrow2x=7\)
\(\Leftrightarrow x=\dfrac{7}{2}=3,5\)
Nếu \(3x< 0\Leftrightarrow x< 0\).Khi đó ta có:
\(-3x=x+7\)
\(\Leftrightarrow-4x=7\)
\(\Leftrightarrow x=-\dfrac{7}{4}\)