Tìm x , biết: a) 1/2 − 3x = − 2/5 ; b) 4/5 = | 2 x − 3 | /2 .

a) \(\frac{1}{2} - 3x = \frac{{ - 2}}{5}\)

          \(3x = \frac{1}{2} + \frac{2}{5}\)

          \(3x = \frac{9}{{10}}\)

           \(x = \frac{3}{{10}}\)

Vậy \(x = \frac{3}{{10}}\).

b) \(\frac{4}{5} = \frac{{\left| {2x - 3} \right|}}{2}\)

    \(\left| {2x - 3} \right| = \frac{8}{5}\)

Trường hợp 1:

\(2x - 3 = \frac{8}{5}\)

     \(2x = \frac{8}{5} + 3\)

     \(2x = \frac{{23}}{5}\)

       \(x = \frac{{23}}{{10}}\)

Vậy \(x \in \left\{ {\frac{{23}}{{10}};\frac{7}{{10}}} \right\}\).

Trường hợp 2:

\(2x - 3 = - \frac{8}{5}\)

     \(2x = - \frac{8}{5} + 3\)

     \(2x = \frac{7}{5}\)

       \(x = \frac{7}{{10}}\)