a)`|5x|=x+2`
`⇔`\(\left[ \begin{array}{l}5x=x+2\\5x=-x-2\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}4x=2\\6x=-2\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=1/2\\x=-1/3\end{array} \right.\)
b)`|-2x|=3x+4`
`⇔`\(\left[ \begin{array}{l}-2x=3x+4\\-2x=-3x-4\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}-5x=4\\x=-4\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=-4/5\\x=-4\end{array} \right.\)