Tim x biết a) $\frac{x}{3}$ – $\frac{10}{21}$ = $\frac{-1}{7}$ b) x-25%x= $\frac{1}{2}$ c)2(x-3)- (3x+2)2 ³

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1. a) `x/3 – 10/21 = -1/7`

   `x/3 = -1/7 + 10/21`

   `x/3= 1/3`

   `x= 1/3 . 3`

   `x= 3/3`

   `x= 1`

   Vậy `x= 1`

   b) `x – 25% x = 1/2`

   `x – 1/4 x = 1/2`

   `x( 1 – 1/4) = 1/2`

   `x. 3/4 = 1/2`

   `x= 1/2 : 3/4`

   `x = 1/2. 4/3`

   `x= 2/3`

   Vậy `x= 2/3`

   c) `2(x-3) – (3x +2) = 2^2`

   `2x – 6 – 3x – 2 = 4`

   `(2x-3x) – (6+2) =4`

   `-x – 8 =4`

   `-x = 4+8`

   `-x = 12`

   `x = -12`

   Vậy `x= -12`

    

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2. Đáp án:

    

   Giải thích các bước giải:

    ` x/3 – 10/21 = -1/7 `

   `x/3 = -1/7 + 10/21 `

   `x/3 = 1/3 `

   `x = 1 `

   vậy `x = 1 `

   ` x – 25%x = 1/2 `

   `x-25/100x=1/2 `

   `x( 1 – 1/4) = 1/2`

   `x. 3/4 = 1/2`

   `x= 1/2 : 3/4`

   `x= 2/3`

   vậy `x = 2/3 `

   `2(x-3) – (3x +2) = 2^2`

   `2x – 6 – 3x – 2 = 4`

   `-x – 8 =4`

   `-x = 4+8`

   `x = -12`

   vậy `x = -12 `

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