_`a)`_
_→ Ta có :_
_$\dfrac{4}{15}$ < $\dfrac{x}{30}$ < $\dfrac{1}{3}$_
_`⇒` 30 . $\dfrac{4}{15}$ < 30 . $\dfrac{x}{30}$ < 30 . $\dfrac{1}{3}$_
_`⇒` 2 . 4 < x < 10_
_`⇒` 8 < x < 10_
_→ Vì x $\in$ Z nên x = 9_
_`→` Vậy x = { 9 }_
_`b)`_
_→ Ta có :_
_$\dfrac{- 5}{12}$ < $\dfrac{x}{9}$ ≤ $\dfrac{2}{- 9}$_
_`⇒` 9 . $\dfrac{- 5}{12}$ < 9 . $\dfrac{x}{9}$ ≤ 9 . $\dfrac{2}{- 9}$_
_`⇒` - 3,75 < x ≤ - 2_
_→ Vì x $\in$ Z nên x = { -2 ; -3 }_
_→ Vậy x = { -2 ; -3 }_
_Câu 4.B :_
_a)_
_→ Ta có :_
_$\dfrac{3}{8}$ < $\dfrac{x}{4}$ < $\dfrac{3}{4}$_
_`⇒` 4 . $\dfrac{3}{8}$ < 4 . $\dfrac{x}{4}$ < 4 . $\dfrac{3}{4}$_
_`⇒` 1,5 < x < 3_
_→ Vì x $\in$ Z nên x = { 2 }_
_→ Vậy x = { 2 }_
_b)_
_→ Ta có :_
_$\dfrac{- 5}{8}$ < $\dfrac{x}{6}$ ≤ $\dfrac{5}{- 10}$_
_`⇒` 6 . $\dfrac{- 5}{8}$ < 6 . $\dfrac{x}{6}$ ≤ 6 . $\dfrac{5}{ - 10}$_
_`⇒` - 3,75 < x ≤ - 3_
_→ Vì x $\in$ Z nên x = { -3 }_
_→ Vậy x = { - 3 }_
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Thưởng th.04.2026
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