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*
2 câu trả lời
${\color{Purple}{\text{Zata}}}$
Đáp án:
↓↓↓
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`
Đáp án:
$\textit{B2: Tìm x biết}$
$\textit{a) 4(18 - 5x) - 12(3x - 7) = 15(2x - 16) - 6(x + 14)}$
$\textit{⇔ 4 . 18 - 4 . 5x - 12 . 3x - 12 . (-7)}$
$\textit{⇔ 15 . 2x- 15 . 16 - 6 . x - 6 . 14}$
$\textit{⇔ 72 - 20x - 36x + 84}$
$\textit{⇔ 30x -240 - 6x - 84}$
$\textit{⇔ 156 - 56x}$
$\textit{⇔ 24x - 324 }$
$\textit{⇔ 56x + 24x}$
$\textit{⇔ 156 + 324}$
$\textit{⇔ 80x ⇒ 480}$
$\textit{x ⇒ 6}$
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$\textit{b) 2(5x - 8) - 3(4x - 5) = 4(3x - 4) + 11}$
$\textit{⇔ 2 . 5x - 2 . 8 - 3 . 4x - 3 . (-5)}$
$\textit{⇔ 4 . 3x - 4 . 4 + 11}$
$\textit{⇔ 10x -16 - 12x + 15}$
$\textit{⇔ 12x - 16 + 11}$
$\textit{⇔ -2x - 1}$
$\textit{⇔ 12x - 5}$
$\textit{⇔ 12x + 2x}$
$\textit{⇔ 1 + 5}$
$\textit{⇔ 14x ⇒ 4}$
$\textit{x ⇒ $\frac{2}{7}$ }$
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