Đáp án:
Bài 12: Tìm x
a, `1/4 - 2x = -1/3`
` 2x = 1/4 - (-1/3)`
` 2x = 7/12`
` x = 7/12 : 2 = 7/24`
b, `4 - 3|x + 2| = -5`
` 3|x + 2| =4 - (-5)`
` 3|x + 2| = 9`
` |x + 2| = 9 : 3`
` |x + 2| = 3`
⇒\(\left[ \begin{array}{l}x + 2 = 3\\x + 2 = - 3\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 3 - 2\\x = - 3 - 2\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 1\\x = - 5\end{array} \right.\)
Vậy `x \in {1 ; -5}`
c, `3(x - 4) - 5(x + 2) = -10`
`3x - 12 - 5x - 10 = - 10`
`(3x - 5x) = -10 + 10 + 12`
`-2x = 12`
` x = 12 : -2`
` x = -6`
d, `(x - 2)^2 - 3(x - 2) = 0`
`(x - 2)(x - 2) - 3(x - 2) = 0`
`(x - 2)(x - 2 - 3) = 0`
`(x - 2)(x - 5) = 0`
⇒\(\left[ \begin{array}{l}x - 2 = 0 \\x - 5 = 0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 0 + 2 \\x = 0 + 5\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 2 \\x = 5\end{array} \right.\)
Vậy `x \in {2 ; 5}`