Bài 2: Tìm x biết a, 4(18 - 5x) - 12(3x - 7) = 15(2x - 16) - 6(x + 14) b, 2(5x - 8) - 3(4x - 5) = 4(3x - 4) + 11. Rúp mình hứa vote 5*

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Đáp án:

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Giải thích các bước giải:

 a)

Ta có $4($ $18$ $-$ $5x$ $)$ $-$ $12($ $3x$ $-$ $7$ $)$ $=$ $15($ $2x$ $-$ $16$ $)$ $-$ $6($ $x$ $+$ $14$ $)$

⇔ $4.18$ $-$ $4.5x$ $-$ $12.3x$ $-$ $12.($ $-$ $7$ $)$ $=$ $15.2x$ $-$ $15.16$ $-$ $6.x$ $-$ $6.14$

⇔ $72$ $-$ $20x$ $-$ $36x$ $+$ $84$ $=$ $30x$ $-$ $240$ $-$ $6x$ $-$ $84$

⇔ $156$ $-$ $56x$ $=$ $24x$ $-$ $324$ ⇔ $56x$ $+$ $24x$ $=$ $156$ $+$ $324$

⇔ $80x$ $=$ $480$ ⇔ $x$ $=$ $6.$

Vậy $x$ $=$ $6.$

b)

Ta có $2($ $5x$ $-$ $8$ $)$ $-$ $3($ $4x$ $-$ $5$ $)$ $=$ $4($ $3x$ $-$ $4$ $)$ $+$ $11$

⇔ $2.5x$ $-$ $2.8$ $-$ $3.4x$ $-$ $3.($ $-$ $5$ $)$ $=$ $4.3x$ $-$ $4.4$ $+$ $11$

⇔ $10x$ $-$ $16$ $-$ $12x$ $+$ $15$ $=$ $12x$ $-$ $16$ $+$ $11$

⇔ $-$ $2x$ $-$ $1$ $=$ $12x$ $-$ $5$ ⇔ $12x$ $+$ $2x$ $=$ $1 + 5$

⇔ $14x$ $=$ $4$ ⇔ $x$ = `2/7`

Vậy giá trị $x$ cần tìm là $x$ = `2/7`