Tìm giá trị của x , biết: (a) x − 2/9 = 5/6 . (b) ( 2/5 − x ) + 7/10 = 7/15 .

a) \[x - \frac{2}{9} = \frac{5}{6}\]

\[x = \frac{5}{6} + \frac{2}{9}\]

\[x = \frac{{19}}{{18}}\].

Vậy \[x = \frac{{19}}{{18}}\].

b) \[\left( {\frac{2}{5} - x} \right) + \frac{7}{{10}} = \frac{7}{{15}}\]

\[\frac{2}{5} - x = \frac{7}{{15}} - \frac{7}{{10}}\]

\[\frac{2}{5} - x = \frac{{ - 7}}{{30}}\]

\[x = \frac{2}{5} - \frac{{ - 7}}{{30}}\]

\[x = \frac{{19}}{{30}}\].

Vậy \[x = \frac{{19}}{{30}}\].