`a, | x - 15 | = 8`
`⇔` $\left[\begin{matrix}x - 15 = 8\\x - 15 = - 8\end{matrix}\right.$
`⇔` $\left[\begin{matrix}x = 23\\x = 7\end{matrix}\right.$
Vậy `, x ∈ { 23 ; 7 } .`
`b, 7 - | x - 3 | = 4`
`⇔ | x - 3 | = 7 - 4`
`⇔ | x - 3 | = 3`
`⇔` $\left[\begin{matrix}x - 3 = 3\\x - 3 = - 3 \end{matrix}\right.$
`⇔` $\left[\begin{matrix}x = 6\\x = 0\end{matrix}\right.$
Vậy `, x ∈ { 6 ; 0 } .`
`c, | 1 - 2x | = 5`
`⇔` $\left[\begin{matrix}1 - 2x = 5\\1 - 2x = - 5\end{matrix}\right.$
`⇔` $\left[\begin{matrix}2x = - 4\\2x = 6\end{matrix}\right.$
`⇔` $\left[\begin{matrix}x = - 2\\x = 3\end{matrix}\right.$
Vậy `, x ∈ { - 2 ; 3 } .`
`d, 8x + 15 - 3x = - 400`
`⇔ x . ( 8 - 3 ) = - 400 - 15`
`⇔ x . 5 = - 415`
`⇔ x = - 415 : 5`
`⇔ x = - 83`
Vậy `, x = - 83 .`
`e, - 32x + 12x - 5x = 900`
`⇔ x . ( - 32 + 12 - 5 ) = 900`
`⇔ x . ( - 25 ) = 900`
`⇔ x = 900 : (- 25 )`
`⇔ x = - 36`
Vậy `, x = - 36 .`
`f, ( x + 2 ) . ( x + 5 ) = 0`
`⇔` $\left[\begin{matrix}x + 2 = 0\\x + 5 = 0\end{matrix}\right.$
`⇔` $\left[\begin{matrix}x = - 2\\x = - 5\end{matrix}\right.$
Vậy `; x ∈ { - 2 ; - 5 } .`
`g, ( x^2 - 25 ) . ( x^2 + 25 ) = 0`
`⇔` $\left[\begin{matrix}x^2 - 25 = 0\\x^2 - 25 = 0\end{matrix}\right.$
`⇔` $\left[\begin{matrix}x^2 = 25\\x^2 = - 25 ( loại )\end{matrix}\right.$
`⇔` $\left[\begin{matrix}x^2 = 5^2\\x^2 = ( - 5 )^2\end{matrix}\right.$
`⇔` $\left[\begin{matrix}x = 5\\x = - 5\end{matrix}\right.$
Vậy `; x ∈ { 5 ; - 5 } .`
