2 câu trả lời
$\textit{Đáp án + Giải thích các bước giải:}$
`|x-9|+3x+2=6`
`=>|x-9|=6-3x-2`
`=>x-9=+-(4-3x)`
$TH1:$ `x \ge 9`
`=>x-9=4-3x`
`=>x+3x=4+9`
`=>4x=13`
`=>x=13/4` $(ktm)$
$TH2:$ `x<9`
`=>x-9=-(4-3x)`
`=>x-9=-4+3x`
`=>x-3x=-4+9`
`=>-2x=5`
`=>x=-5/2` $(tm)$
Vậy `x=-5/2`
#andy
\[\begin{array}{l}
\left| {x - 9} \right| + 3x + 2 = 6\left( {DKXD:x \ge 9} \right)\\
\Leftrightarrow \left| {x - 9} \right| + 3x = 4\\
\Leftrightarrow \left| {x - 9} \right| = 4 - 3x\\
\Leftrightarrow \left[ \begin{array}{l}
x - 9 = 4 - 3x\\
x - 9 = - 4 + 3x
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x + 3x = 4 + 9\\
x - 3x = - 4 + 9
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
4x = 13\\
- 2x = 5
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{{13}}{4}\left( {TMDK} \right)\\
x = - \dfrac{5}{2}\left( {KTMDK} \right)
\end{array} \right.\\
\Rightarrow S = \left\{ {\dfrac{{13}}{4}} \right\}
\end{array}\]
