Tìm x biết : a; -(754+x)=(x-12-741)-23 b; 9x + 34 =- (2x -56) c; 2 – |x-5|=-7 d; (x-12)=(2x+31)-6

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1. Đáp án + Giải thích các bước giải:

   Ta có :

   `a,-(754+x)=(x-12-741)-23`

   `→-754-x=x-12-741-23`

   `→-x-x=754-12-741-23`

   `→-2x=-22`

   `→x=11`

   `——–`

   `b,9x+34=-(2x-56)`

   `→9x+34=-2x+56`

   `→9x+2x=-34+56`

   `→11x=22`

   `→x=2`

   `——–`

   `c,2-|x-5|=-7`

   `→|x-5|=2-(-7)`

   `→|x-5|=9`

   `→` \(\left[ \begin{array}{l}x-5=9\\x-5=-9\end{array} \right.\) 

   `→` \(\left[ \begin{array}{l}x=14\\x=-4\end{array} \right.\) 

   Vậy `x∈{14;-4}`

   `——–`

   `d,(x-12)=(2x+31)-6`

   `→x-12=2x+31-6`

   `→x-2x=12+31-6`

   `→-x=37`

   `→x=-37`

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2. `a)-(754+x)=(x-12-741)-23`

   `⇒-754-x=x-12-741-23`

   `⇒-754-x=x-776`

   `⇒-x-x=-776+754`

   `⇒-2x=-22`

   `⇒x=11`

   Vậy `x=11`

   `b)9x + 34 =- (2x -56)`

   `⇒9x+34=-2x+56`

   `⇒9x+2x=56-34`

   `⇒11x=22`

   `⇒x=22:11`

   `⇒x=2`

   Vậy `x=2`

   `c)2 – |x-5|=-7`

   `⇒|x-5|=2-(-7)`

   `⇒|x-5|=9`

   `⇒` \(\left[ \begin{array}{l}x-5=9\\x-5=-9\end{array} \right.\) 

   `⇒` \(\left[ \begin{array}{l}x=14\\x=-4\end{array} \right.\) 

   Vậy `x∈{14;-4}`

   `d)(x-12)=(2x+31)-6`

   `⇒x-12=2x+31-6`

   `⇒x-2x=31-6+12`

   `⇒-x=37`

   `⇒x=-37`

   Vậy `x=-37`

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