Tìm x, biết: a) 1/6 - x = - 1/42

a) \(\frac{1}{6} - x = \frac{{ - 1}}{{42}}\)

\(x = \frac{1}{6} - \frac{{ - 1}}{{42}}\)

\(x = \frac{7}{{42}} + \frac{1}{{42}}\)

\(x = \frac{8}{{42}}\)

\(x = \frac{4}{{21}}\)

Vậy \(x = \frac{4}{{21}}.\)

b) \[0,55 + 0,45:x = - 0,35\]

 \[0,45:x = - 0,35 - 0,55\]

 \[0,45:x = - 0,9\]

 \[x = 0,45:\left( { - 0,9} \right)\]

 \[x = - 0,5\]

Vậy \[x = - 0,5.\]

c) \[ - \frac{3}{4}x + \frac{1}{4}\left( {x - 1} \right) = - \frac{{12}}{5}\]

\[ - \frac{3}{4}x + \frac{1}{4}x - \frac{1}{4} = - \frac{{12}}{5}\]

\[\left( { - \frac{3}{4} + \frac{1}{4}} \right)x - \frac{1}{4} = - \frac{{12}}{5}\]

\[ - \frac{1}{2}x = - \frac{{12}}{5} + \frac{1}{4}\]

\[ - \frac{1}{2}x = - \frac{{48}}{{20}} + \frac{5}{{20}}\]

\[ - \frac{1}{2}x = - \frac{{43}}{{20}}\]

\[x = - \frac{{43}}{{20}}:\left( { - \frac{1}{2}} \right)\]

\[x = \frac{{43}}{{10}}\]

Vậy \[x = \frac{{43}}{{10}}.\]