Tìm x của biểu thức, biết: a) 8/5 − 3/5 : x = 0 , 4 ; b) 4/5 − ∣ ∣ x − 1/2 ∣ ∣ = 3/4 .

a) \(\frac{8}{5} - \frac{3}{5}:x = 0,4\)

     \(\frac{3}{5}:x = \frac{8}{5} - \frac{2}{5} = \frac{6}{5}\)

     \(x = \frac{3}{5}:\frac{6}{5}\)

     \(x = \frac{3}{5}.\frac{5}{6} = \frac{1}{2}\)

Vậy \(x = \frac{1}{2}\).

b) \(\frac{4}{5} - \left| {x - \frac{1}{2}} \right| = \frac{3}{4}\)

     \(\left| {x - \frac{1}{2}} \right| = \frac{4}{5} - \frac{3}{4}\)

     \(\left| {x - \frac{1}{2}} \right| = \frac{{16}}{{20}} - \frac{{15}}{{20}} = \frac{1}{{20}}\)

Trường hợp 1:

\(x - \frac{1}{2} = \frac{1}{{20}}\)

\(x = \frac{1}{{20}} + \frac{1}{2}\)

\(x = \frac{1}{{20}} + \frac{{10}}{{20}} = \frac{{11}}{{20}}\)

Vậy \(x \in \left\{ {\frac{{11}}{{20}};\frac{9}{{20}}} \right\}\).

Trường hợp 2:

\(x - \frac{1}{2} = - \frac{1}{{20}}\)

\(x = - \frac{1}{{20}} + \frac{1}{2}\)

\(x = - \frac{1}{{20}} + \frac{{10}}{{20}} = \frac{9}{{20}}\)