a) 3(x + 7 ) +9 = 9 – 2 ( x + 5 ) b) 218 – ( x + 31 = x – 29

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1. `\text{~~Holi~~}`

   `a. 3(x+7)+9=9-2(x+5)`

   `-> 3x+21+9=9-2x-10`

   `-> 3x+21+9-9+2x+10=0`

   `-> 5x+31=0`

   `-> 5x=-31`

   `-> x=-31/5`

   Vậy `x=-31/5`

   `b. 218-(x+31)=x-29`

   `-> 218-x-31=x-29`

   `-> 218-x-31-x+29=0`

   `-> 216-2x=0`

   `-> 2x=216`

   `-> x=216/2`

   `-> x=108`

   Vậy `x=108`

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2. `a) 3(x + 7 ) +9 = 9 – 2 ( x + 5 )`

   `⇔3x+21+9=9-2x-10`

   `⇔3x+2x=9-9-10-21`

   `⇔5x=-31`

   `⇔x=-{31}/5`

   `b) 218 – ( x + 31) = x – 29`

   `⇔218-x-31=x-29`

   `⇔-x-x=-29+31-218`

   `⇔-2x=-216`

   `⇔x={-216}/{-2}`

   `⇔x=108`

    

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