Tìm x, biết: a) (2x–5)+17=6 b) 10–2(4–3x)=-4 c) -12+3(-x+7)=-18 d) x.(x+7)=0

Đáp án:

$a)$  $x=-3$

$b)$ $x=-1$

$c)$ $x=9$

$d)$ $\text{x $\in$}$ $\left\{0;-7\right\}$

Giải thích các bước giải:

$a)$ $\left(2x-5\right)+17=6$

$⇒2x-5+17=6$

$⇒2x+12=6$

$⇒2x=6-12$

$⇒2x=-6$

$⇒x=-3$

`Vậy` $x=-3$

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$b)$ $10-2\left(4-3x\right)=-4$

$⇒−2\left(4−3x\right)=−4−10$

$⇒-2\left(4-3x\right)=-14$

$⇒4-3x=7$

$⇒−3x=7−4$

$⇒-3x=3$

$⇒x=-1$

`Vậy` $x=-1$

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$c)$ $-12+3\left(-x+7\right)=-18$

$⇒−12+3\left(7−x\right)=−18$

$⇒3\left(7−x\right)−12=−18$

$⇒3\left(7-x\right)=-6$

$⇒7-x=-2$

$⇒−x=−2−7$

$⇒-x=-9$

$⇒x=9$

`Vậy` $x=9$

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$d)$ $x. \left(x+7\right)=0$

$⇒\left[ \begin{array}{l}x=0\\\:x+7=0\end{array} \right.$

$⇒\left[ \begin{array}{l}x=0\\x=-7\end{array} \right.$ 

$\text{Vậy x $\in$}$ $\left\{0;-7\right\}$