Tìm x , biết:  a) x + 2/5 = 5/2

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

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

\(x = \frac{1}{{12}}\).

Vậy \(x = \frac{1}{{12}}\).

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

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

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

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

Vậy \(x = \frac{1}{6}\).

c) \({\left( {1 - 2x} \right)^3} = - 8\)

\({\left( {1 - 2x} \right)^3} = {\left( { - 2} \right)^3}\)

\(1 - 2x = - 2\)

\(2x = 1 - \left( { - 2} \right)\)

\(2x = 3\)

\(x = \frac{3}{2}\).

Vậy \(x = \frac{3}{2}\).