Tìm x a) 7/8 + x = 3/5 b) 2/3(2x - 1) = - 4/21

a) \(\frac{7}{8} + x = \frac{3}{5}\)

\(x = \frac{3}{5} - \frac{7}{8}\)

\(x = \frac{{24}}{{40}} - \frac{{35}}{{40}}\)

\(x = \frac{{24 - 35}}{{40}}\)

\(x = \frac{{ - 11}}{{40}}\)

b) \(\frac{2}{3}\left( {2x - 1} \right) = \frac{{ - 4}}{{21}}\)

\[2x - 1 = \frac{{ - 4}}{{21}}:\frac{2}{3}\]

\[2x - 1 = \frac{{ - 4}}{{21}}.\frac{3}{2}\]

\[2x - 1 = \frac{{ - 2}}{7}\]

\[2x = \frac{{ - 2}}{7} + 1\]

\[2x = \frac{5}{7}\]

\[x = \frac{5}{7}:2\]

\[x = \frac{5}{7}.\frac{1}{2}\]

\[x = \frac{5}{{14}}\]