Tìm giá trị của x biết: (a) 2/7 + x = 5/8 . (b) − 4/3 + 1/3 x = 3/4 .

a) \(\frac{2}{7} + x = \frac{5}{8}\,\)

\(x = \frac{5}{8} - \frac{2}{7}\)

\(x = \frac{{19}}{{56}}.\)

Vậy \(x = \frac{{19}}{{56}}.\)

b) \[\frac{{ - 4}}{3} + \frac{1}{3}x = \frac{3}{4}\,\]

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

\[\frac{1}{3}x = \frac{{25}}{{12}}\]

\[x = \frac{{25}}{{12}}:\frac{1}{3}\]

\[x = \frac{{25}}{4}.\]

Vậy \[x = \frac{{25}}{4}.\]