Tìm x , biết: a) 2x + 2/5 = − 2/5 ; b) (3x − 7)/ 8 = 5/ 2 ;

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

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

\(2x = \frac{{ - 4}}{5}\)

\(x = \frac{{ - 4}}{5}:2\)

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

Vậy \(x = - \frac{2}{5}\)

b) \(\frac{{3x - 7}}{8} = \frac{5}{2}\)

     \(2.\left( {3x - 7} \right) = 8.5\)

     \(6x - 14 = 40\)

              \(6x = 54\)

                \(x = 54:6\)

                 \(x = 9\)

Vậy \(x = 9\).

c) \(\left| {x - \frac{2}{3}} \right| - 2 = - 0,5\)

    \(\left| {x - \frac{2}{3}} \right| = - 0,5 + 2 = 1,5\)

Trường hợp 1: \(x - \frac{2}{3} = 1,5\) \(x = \frac{3}{2} + \frac{2}{3}\) \(x = \frac{{13}}{6}\) Vậy \(x \in \left\{ {\frac{{13}}{6};\frac{{ - 5}}{6}} \right\}\).

Trường hợp 2: \(x - \frac{2}{3} = - 1,5\) \(x = \frac{{ - 3}}{2} + \frac{2}{3}\) \(x = \frac{{ - 5}}{6}\)