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4.\(\dfrac{1}{7}\) ????

hello

1/7 mà sao lại 17

Ai đúng vậy các bn

\(x:\dfrac{1}{7}=14\)

<=> \(\dfrac{1}{7x}=14\)

ĐKXĐ: x\(\ne\)0

<=> 1 = 14 . 7x

<=> 98x =1

<=> x = \(\dfrac{1}{98}\)

a. x + \(\dfrac{2}{5}\) = \(\dfrac{1}{2}\)

\(\Leftrightarrow\dfrac{10x}{10}+\dfrac{4}{10}=\dfrac{5}{10}\)

<=> 10x + 4 = 5

<=> 10x = 1

<=> x = \(\dfrac{1}{10}\)

b. \(x-\dfrac{2}{5}=\dfrac{1}{7}\)

\(\Leftrightarrow\dfrac{35x}{35}-\dfrac{14}{35}=\dfrac{5}{35}\)

<=> 35x - 14 = 5

<=> 35x = 19 

<=> x = \(\dfrac{19}{35}\)

c. \(x.\dfrac{3}{4}=\dfrac{9}{20}\)

\(\Leftrightarrow\dfrac{15x}{20}=\dfrac{9}{20}\)

<=> 15x = 9

<=> x = \(\dfrac{9}{15}\)

d. \(x:\dfrac{1}{7}=14\)

\(\Leftrightarrow\dfrac{1}{7x}=14\)

ĐKXĐ: x\(\ne\)0

<=> 14 . 7x = 1

<=> 98x = 1

<=> x = \(\dfrac{1}{98}\)(thỏa mãn)

e. \(\dfrac{2}{3}-x=\dfrac{1}{5}\)

\(\Leftrightarrow\dfrac{10}{15}-\dfrac{15x}{15}=\dfrac{3}{15}\)

<=> 10 - 15x = 3

<=> 10 - 3 = 15x

<=> 15x = 7

<=> x = \(\dfrac{7}{15}\)

f. \(\dfrac{4}{15}:x=\dfrac{12}{25}\)

\(\Leftrightarrow\dfrac{4}{15x}=\dfrac{12}{25}\)

ĐKXĐ: x \(\ne\) 0

<=> 14 . 25 = 12 . 15x

<=> 100 = 180x

<=> x = \(\dfrac{100}{180}=\dfrac{5}{9}\)

Ai, người hỏi hay người trả lời