Bài 2: Tìm x a) x + 3/21 = 8/7 b) |x+2| – 1/3 = 5/6 c) 4/5 – 1/3 . ( x+ 3/2 ) = 7/15

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1. a, `x + 3/21 = 8/7`

       `x + 1/7   = 8/7`

       `x             = 8/7 – 1/7`

       `x             = 1`

     Vậy `x=1`

   b, `|x+2| – 1/3 = 5/6`

       `|x+2|          = 5/6 + 2/6`

       `|x+2|          = 7/6`

   `=>` \(\left[ \begin{array}{l}x+2=\frac{7}{6}\\x+2=\frac{-7}{6}\end{array} \right.\) 

   `=>` \(\left[ \begin{array}{l}x=\frac{-5}{6}\\x=\frac{-19}{6}\end{array} \right.\)

     Vậy \(\left[ \begin{array}{l}x=\frac{-5}{6}\\x=\frac{-19}{6}\end{array} \right.\) 

   c, `4/5 – 1/3 . ( x + 3/2 ) = 7/15`

               `1/3 . ( x + 3/2 ) = 4/5 – 7/15`

               `1/3 . ( x + 3/2 ) = 1/3`

                          `x + 3/2   = 1`

                          `x             = -1/2`

       Vậy `x=-1/2`

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2. Đáp án:

    `x=1`

   `x\in{-5/6;-19/6}`

   `x=-1/2`

   Giải thích các bước giải:

    `x+ 3/21 = 8/7`

   `x = 8/7 – 3/21 `

   `x= 8/7 – 1/7 `

   `x=(8-1)/7`

   `x=7/7`

   `x=1 `

   vậy `x=1` 

   `|x+2| – 1/3 = 5/6 `

   `|x+2 | = 5/6 + 1/3 `

   `|x+2| = 7/6 `

   \(\left[ \begin{array}{l}x+2= \dfrac{7}{6}\\x+2= \dfrac{-7}{6}\end{array} \right.\) 

   \(\left[ \begin{array}{l}x= \dfrac{7}{6}-2\\x= \dfrac{-7}{6}-2\end{array} \right.\) 

   \(\left[ \begin{array}{l}x= \dfrac{-5}{6}\\x= \dfrac{-19}{6}\end{array} \right.\) 

   vậy `x\in{-5/6;-19/6}`

   `4/5 – 1/3 . ( x+ 3/2 ) = 7/15`

   ` 1/3.(x+3/2) = 4/5 – 7/15 `

   ` 1/3.(x+3/2)=1/3 `

   `x+3/2 = 1/3  :1/3 `

   `x+3/2 = 1 `

   `x = 1-3/2 `

   `x=-1/2`

   vậy `x=-1/2`

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