x phần 3 = 2 phần 3 + -1 phần 7

Đáp án:

 $\dfrac{x}{3}=\dfrac{2}{3}+\dfrac{-1}{7}$

$⇔ \dfrac{x}{3}= \dfrac{14}{21}+\dfrac{-3}{21}$

$⇔ \dfrac{x}{3}= \dfrac{11}{21}$

$⇔ x.21= 3.11$

$⇔ x= \dfrac{3.11}{21}$

$⇔ x= \dfrac{11}{7}$

$\text{Vậy x=}$ $\dfrac{11}{7}$

$\dfrac{x}{3}=\dfrac{2}{3}+\dfrac{-1}{7}$

$⇒ \dfrac{x}{3.7}=\dfrac{2.7}{3.7}+\dfrac{-1.3}{7.3}$

$⇒ \dfrac{x}{21}=\dfrac{14}{21}+\dfrac{-3}{21}$

$⇒ \dfrac{x}{21}=\dfrac{14+(-3)}{21}$

$⇒ \dfrac{x}{21}=\dfrac{14-3}{21}$

$⇒ \dfrac{x}{21}=\dfrac{11}{21}$

$⇒ x=11$

Vậy $x=1$

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