Câu hỏi của huỳnh phú bình

Question

tìm x thuộc N,biết 2/7 < x/3 < 5/4

Huỳnh Quang Sang · Accepted Answer

$\frac{2}{7}< \frac{x}{3}< \frac{5}{4}$

$MSC=BCNN(7,3,4)=84$

Ta quy đồng ra : $\frac{2\cdot12}{84}< \frac{x\cdot28}{84}< \frac{5\cdot21}{84}$

$\Rightarrow\frac{24}{84}< \frac{28x}{84}< \frac{105}{84}$

$\Rightarrow24< 28x< 105$

$\Rightarrow x\in\left\{1;2;3\right\}$

Vậy : ....

Câu trả lời:

$\frac{2}{7}< \frac{x}{3}< \frac{5}{4}$

$MSC=BCNN(7,3,4)=84$

Ta quy đồng ra : $\frac{2\cdot12}{84}< \frac{x\cdot28}{84}< \frac{5\cdot21}{84}$

$\Rightarrow\frac{24}{84}< \frac{28x}{84}< \frac{105}{84}$

$\Rightarrow24< 28x< 105$

$\Rightarrow x\in\left\{1;2;3\right\}$

Vậy : ....

Trần Tiến Pro ✓ · Answer

$\frac{2}{7}< \frac{x}{3}< \frac{5}{4}$

$\Rightarrow\frac{24}{84}< \frac{28x}{84}< \frac{105}{84}$

$\Rightarrow24< 28x< 105$

$\Rightarrow x\ge1$

$\text{+) Nếu }x=1:24< 28.1< 105\left(TM\right)$

$\text{+) Nếu }x=2:24< 28.2< 105=24< 56< 105\left(TM\right)$

$\text{+) Nếu }x=3:24< 28.3< 105=24< 84< 105\left(TM\right)$

$\text{+) Nếu }x=4:24< 28.4< 105=24< 112< 105\left(KTM\right)$

$\text{Vậy x }\in\left\{1;2;3\right\}$

Câu trả lời:

$\frac{2}{7}< \frac{x}{3}< \frac{5}{4}$

$\Rightarrow\frac{24}{84}< \frac{28x}{84}< \frac{105}{84}$

$\Rightarrow24< 28x< 105$

$\Rightarrow x\ge1$

$\text{+) Nếu }x=1:24< 28.1< 105\left(TM\right)$

$\text{+) Nếu }x=2:24< 28.2< 105=24< 56< 105\left(TM\right)$

$\text{+) Nếu }x=3:24< 28.3< 105=24< 84< 105\left(TM\right)$

$\text{+) Nếu }x=4:24< 28.4< 105=24< 112< 105\left(KTM\right)$

$\text{Vậy x }\in\left\{1;2;3\right\}$