Tìm giá trị của x biết: (a) 3/4 − x = 1/3 . (b) 1/2 x + 3/2 = − 3/10 .

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

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

\[x = \frac{9}{{12}} - \frac{4}{{12}}\]

\[x = \frac{5}{{12}}\]

Vậy \[x = \frac{5}{{12}}\].

b) \[\frac{1}{2}x + \frac{3}{2} = \frac{{ - 3}}{{10}}\]

\[\frac{1}{2}x = \frac{{ - 3}}{{10}} - \frac{3}{2}\]

\[\frac{1}{2}x = \frac{{ - 3}}{{10}} - \frac{{15}}{{10}}\]

\[\frac{1}{2}x = \frac{{ - 18}}{{10}}\]

\[x = \frac{{ - 18}}{{10}}:\frac{1}{2}\]

\[x = \frac{{ - 18}}{{10}}.2\]

\[x = \frac{{ - 18}}{5}\]

Vậy \[x = \frac{{ - 18}}{5}\].

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

\[\left( {x + 3} \right).3 = 4\]

\[3x + 9 = 4\]

\[3x = 4 - 9\]

\[3x = - 5\]

\[x = \frac{{ - 5}}{3}\]

Vậy \[x = \frac{{ - 5}}{3}\].