Tìm x: a)- 1/2:x = 1/3;  

a) \[\frac{{ - 1}}{2}:x = \frac{1}{3}\]

\[x = \frac{{ - 1}}{2}:\frac{1}{3}\]

\[x = \frac{{ - 1}}{2}.3\]

\[x = \frac{{ - 3}}{2}\]

Vậy \[x = \frac{{ - 3}}{2}\]

b) \[\frac{2}{3}x + \frac{1}{2} = \frac{3}{4}\]

\[\frac{2}{3}x = \frac{3}{4} - \frac{1}{2}\]

\[\frac{2}{3}x = \frac{1}{4}\]

\[x = \frac{1}{4}:\frac{2}{3}\]

\[x = \frac{3}{8}\]

Vậy \[x = \frac{3}{8}\].