a)

\(\dfrac{2}{3}\cdot x-\dfrac{4}{7}=\dfrac{1}{8}\\ \dfrac{2}{3}\cdot x=\dfrac{1}{8}+\dfrac{4}{7}\\ \dfrac{2}{3}\cdot x=\dfrac{39}{56}\\ x=\dfrac{39}{56}:\dfrac{2}{3}\\ x=\dfrac{117}{112}\)

b)

\(\dfrac{2}{7}-\dfrac{8}{9}\cdot x=\dfrac{2}{3}\\ \dfrac{8}{9}\cdot x=\dfrac{2}{7}-\dfrac{2}{3}\\ \dfrac{8}{9}\cdot x=-\dfrac{8}{21}\\ x=-\dfrac{8}{21}:\dfrac{8}{9}\\ x=-\dfrac{3}{7}\)

c)

\(\dfrac{4}{7}+\dfrac{5}{9}:x=\dfrac{1}{5}\\ \dfrac{5}{9}:x=\dfrac{1}{5}-\dfrac{4}{7}\\ \dfrac{5}{9}:x=-\dfrac{13}{35}\\ x=\dfrac{5}{9}:\left(-\dfrac{13}{35}\right)\\ x=-\dfrac{175}{117}\)

Lấy máy tính ra ấn là đc mà bạn

A.

\(\dfrac{2}{3}x-\dfrac{4}{7}=\dfrac{1}{8}\)

<=>\(\dfrac{2}{3}x=\dfrac{1}{8}+\dfrac{4}{7}\)

<=>\(\dfrac{2}{3}x=\dfrac{39}{56}\)

<=> \(\dfrac{2}{3}x.\dfrac{3}{2}=\dfrac{39}{56}.\dfrac{3}{2}\)

<=> x= \(\dfrac{117}{112}\)

B.

\(\dfrac{2}{7}-\dfrac{8}{9}x=\dfrac{2}{3}\)

<=> \(\dfrac{-8}{9}x=\dfrac{2}{3}-\dfrac{2}{7}\)

<=> \(\dfrac{-8}{9}x=\dfrac{8}{21}\)

<=> \(\dfrac{-8}{9}x.\dfrac{-9}{8}=\dfrac{8}{21}.\dfrac{-9}{8}\)

<=> x= \(\dfrac{-3}{7}\)

C.

\(\dfrac{4}{7}+\dfrac{5}{9}:x=\dfrac{1}{5}\)

\(\dfrac{5}{9}:x=\dfrac{1}{5}-\dfrac{4}{7}\)

<=>\(\dfrac{5}{9}.\dfrac{1}{x}=\dfrac{-13}{35}\)

<=> \(\dfrac{5}{9x}=\dfrac{-13}{35}\)

<=> 9x= \(\dfrac{5.35}{-13}\)

<=> 9x = \(\dfrac{-175}{13}\)

<=> \(9x.\dfrac{1}{9}=\dfrac{-175}{13}.\dfrac{1}{9}\)

<=> x= \(\dfrac{-175}{117}\)