Tìm x , biết:  a) 5/2 : x = -5/4

a)  \[\frac{5}{8}:x = \frac{{ - 5}}{4}\]\(x = \frac{5}{8}:\frac{{ - 5}}{4}\)\(\begin{array}{l}x = \frac{5}{8}.\frac{{ - 4}}{5}\\x = \frac{{ - 1}}{2}\end{array}\)b) \[\frac{2}{5}.\frac{3}{5} + x = {\left( {\frac{4}{5}} \right)^2}\] \[\frac{6}{{25}} + x = \frac{{16}}{{25}}\]\[x = \frac{{16}}{{25}} - \frac{6}{{25}} = \frac{{10}}{{25}} = \frac{2}{5}\]c) \[\frac{5}{8} + \frac{3}{8} \cdot x = {\left( {\frac{{ - 1}}{2}} \right)^3}\] \[\frac{3}{8} \cdot x = \frac{{ - 1}}{8} - \frac{5}{8} = \frac{{ - 6}}{8}\]\[x = \frac{{ - 6}}{8}:\frac{3}{8} =  - 2\]