Bài 2. (2,0 điểm) Tìm x, a) $\frac{2}{5} -x=0,1$ b) $\frac{1}{2}. ( x-\frac{1}{2}) + \frac{3}{4}= 3$ c) $\frac{1}{2}. ( x-2) + \frac{1}{3}( 2-x) = x$ 

Đáp án + Giải thích các bước giải:

    `a) 2/5 - x = 0,1`

`<=> 2/5 - x = 1/10`

`<=> -x = 1/10 - 2/5`

`<=> -x = 1/10 - 4/10`

`<=> -x = (1 - 4)/10`

`<=> -x = (-3)/10`

`<=> -x · (-1) = (-3)/10 · (-1)`

`<=> x = 3/10`

Vậy `x = 3/10`

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    `b) 1,2 · (x - 1/2) + 3/4 = 3`

`<=> 6/5 · (x - 1/2) = 3 - 3/4`

`<=> 6/5 · (x - 1/2) = 12/4 - 3/4`

`<=> 6/5 · (x - 1/2) = (12 - 3)/4`

`<=> 6/5 · (x - 1/2) = 9/4`

`<=> x - 1/2 = 9/4 ÷ 6/5`

`<=> x - 1/2 = 9/4 · 5/6`

`<=> x - 1/2 = 15/8`

`<=> x = 15/8 + 1/2`

`<=> x = 15/8 + 4/8`

`<=> x = (15 + 4)/8`

`<=> x = 19/8`

Vậy `x = 19/8`

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    `c) 1/2 · (x - 2) + 1/3 · (2 - x) = x`

`<=> 1/2 · (x - 2) - 1/3 · (x - 2) = x`

`<=> (x - 2)(1/2 - 1/3) = x`

`<=> (x - 2)(3/6 - 2/6) = x`

`<=> (x - 2) · (3 - 2)/6 = x`

`<=> (x - 2) · 1/6 = x`

`<=> x - 2 = x ÷ 1/6`

`<=> x - 2 = x · 6`

`<=> 6x = x - 2`

`<=> 6x - x = -2`

`<=> 5x = -2`

`<=> x = (-2)/5`

Vậy `x = (-2)/5`

~MioWiky~