Tìm x , biết: a) x + 4/ 5 = 1/ 3 ; b) 2/ 3 = | 1 − 5 x | /11 .

a) \(x + \frac{4}{5} = \frac{1}{3}\)

          \(x = \frac{1}{3} - \frac{4}{5}\)

          \(x = \frac{5}{{15}} - \frac{{12}}{{15}}\)

          \(x = - \frac{7}{{15}}\)

Vậy \(x = - \frac{7}{{15}}\).

b) \(\frac{2}{3} = \frac{{\left| {1 - 5x} \right|}}{{11}}\)

    \(\left| {1 - 5x} \right| = \frac{{2.11}}{3} = \frac{{22}}{3}\)

Trường hợp 1:

\(1 - 5x = \frac{{22}}{3}\)

     \(5x = 1 - \frac{{22}}{3}\)

     \(5x = - \frac{{19}}{3}\)

       \(x = - \frac{{19}}{{15}}\)

Vậy \(x \in \left\{ { - \frac{{19}}{{15}};\frac{5}{3}} \right\}\).

Trường hợp 2:

\(1 - 5x = - \frac{{22}}{3}\)

      \(5x = 1 - \left( { - \frac{{22}}{3}} \right)\)

     \(5x = \frac{{25}}{3}\)

       \(x = \frac{5}{3}\)