`a)`
`|x|+7=9`
`to |x|=9-7`
`to |x|=2`
`to` \(\left[ \begin{array}{l}x=2\\x=-2\end{array} \right.\)
Vậy `x in {-2;2}`
`b)`
`|x-5|=8`
`to` \(\left[ \begin{array}{l}x-5=8\\x-5=-8\end{array} \right.\) `to` \(\left[ \begin{array}{l}x=13\\x=-3\end{array} \right.\)
Vậy `x in {-3;13}`