1) Tìm x thuộc Z, biết A) x-(-15)=3 B)20-(x+12)=0 C)(5-x)-(-25+7) = -3+12 D)|x+5|=2-(4-5)

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1.  `x – (-15)=3 `

   `x=3 + (-15)`

   `x=-(15-3)`

   `x=-12 `

   Vậy `x=-12 `

   `b) 20-(x+12)=0`

   `x+12 = 20 – 0 `

   `x+12 = 20`

   `x=20 – 12 `

   `x=8`

   Vậy `x=8`

   `c) (5-x) – (-25+7) = -3+12 `

   `(5-x) – (-18)=9`

   `5-x = 9 + (-18)`

   `5-x=-(18-9)`

   `5-x=-9`

   `x= 5 – (-9)`

   `x=5+9`

   `x=14 `

   vậy `x=14 `

   `|x+5|=2-(4-5)`

   `|x+5|=2-(-1)`

   `|x+5|=2+1 `

   `|x+5|=3 `

   `TH1 : x+5 = 3 `

   `x=3-5 `

   `x=-2 `

   `TH2 : x+5 = -3 `

   `x=-3-5 `

   `x=-3+(-5) `

   `x=-8 `

   Vậy `x\in{-2;-8}`

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2. `a) x-(-15)=3`

   `→x+15=3`

   `→x=3-15`

   `→x=-12`

   Vậy `x=-12`

   `b)20-(x+12)=0`

   `→x+12=20-0`

   `→x+12=20`

   `→x=20-12`

   `→x=8`

   Vậy `x=8`

   `c)(5-x)-(-25+7) = -3+12`

   `→5-x-(-18)=9`

   `→5-x+18=9`

   `→5-x=9-18`

   `→5-x=-9`

   `→x=5-(-9)`

   `→x=14`

   Vậy `x=14`

   `d)|x+5|=2-(4-5)`

   `→|x+5|=2-(-1)`

   `→|x+5|=3`

   `→` \(\left[ \begin{array}{l}x+5=3\\x+5=-3\end{array} \right.\) 

   `→` \(\left[ \begin{array}{l}x=-2\\x=-8\end{array} \right.\) 

   Vậy `x∈{-2;-8}`

    

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