Tìm 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 ²

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1. Đáp án+Giải thích các bước giải:

    `a)x/3-10/21=-1/7`

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

   `\to x/3=-3/21+10/21`

   `\to x/3=(-3+10)/21`

   `\to x/3=7/21`

   `\to x/3=1/3`

   `\to 3x=3`

   `\to x=3:3`

   `\to x=1`

   Vậy `x=1`

   `b)x-25%x=1/2`

   `\to x-(25)/(100)x=1/2`

   `\to x-1/4x=1/2`

   `\to (1-1/4)x=1/2`

   `\to 3/4x=1/2`

   `\to x=1/2:3/4`

   `\to x=1/(2).(4)/3`

   `\to x=2/3`

   Vậy `x=2/3`

   `c)2(x-3)-(3x+2)=2^2`

   `\to 2(x-3)-(3x+2)=4`

   `\to 2x-6-3x-2=4`

   `\to (2x-3x)+(-6-2)=4`

   `\to -x-8=4`

   `\to -x=4+8`

   `\to -x=12`

   `\to x=-12`

   Vậy `x=-12`

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2. 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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