1) 3(x - 4) - (8 - x) = 12
3x - 12 - 8 + x = 12
4x - 20 = 12
4x = 12 + 20
4x = 32
x = 8
2) 5(x - 6) - 2(x + 3) = 12
5x - 30 - 2x - 6 = 12
3x - 36 = 12
3x = 12 + 36
3x = 48
x = 16
3) 5 - | x + 7| = 4
|x + 7| = 4 - 5
|x + 7| = -1 x + 7 = 1; -1 x + 7 = 1 hoặc x + 7 = -1 x = 1 - 7 x = -1 - 7 x = -6 x = -8 => x = -6 hoặc x = -8 4) 6|x - 7| = 18 : (-3) 6|x - 7| = -6 6|x - 7| = -6 : 6 |x - 7| = -1 x - 7 = 1; -1 x - 7 = 1 hoặc x - 7 = -1 x = 1 + 7 x = -1 + 7 x = 8 x = 6 => x = 8 hoặc x = 6
1, \(3.\left(x-4\right)-\left(8-x\right)=12\)
\(\Leftrightarrow3x-12-8+x=12\)
\(\Leftrightarrow3x+x=12+12+8\)
\(\Leftrightarrow4x=32\)
\(\Leftrightarrow x=8\)
Vậy : \(x=8\)
2, \(5.\left(x-6\right)-2.\left(x+3\right)=12\)
\(\Leftrightarrow5x-30-2x-6=12\)
\(\Leftrightarrow5x-2x=12+30+6\)
\(\Leftrightarrow3x=48\)
\(\Leftrightarrow x=\frac{48}{3}=16\)
Vậy : \(x=16\)
3, \(5-\left|x+7\right|=4\)
\(\Leftrightarrow\left|x+7\right|=5-4=1\)
\(\Leftrightarrow\left[{}\begin{matrix}x+7=1\\x+7=-1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-8\end{matrix}\right.\)
Vậy : \(x\in\left\{6,-8\right\}\)
4, \(6.\left|x-7\right|=18:\left(-3\right)\)
\(\Leftrightarrow6.\left|x-7\right|=-6\)
\(\Leftrightarrow\left|x-7\right|=-1\)
Ta thấy : \(\left|x-7\right|\ge0\forall x\) mà \(-1< 0\)
\(\Rightarrow x\in\varnothing\)
Vậy : không có \(x\) thỏa mãn đề.