Tìm \(x,\) biết: a) \(\frac{1}{6} - x = \frac{{ - 1}}{{42}}.\)                       b) \[0,55 + 0,45:x =  - 0,35.\]                                              c) \(\frac{1}{2}\left( {x

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

\(\frac{1}{2}x - \frac{1}{3} - \frac{2}{3}x + 1 - x = 0\)

\(\left( {\frac{1}{2}x - \frac{2}{3}x - x} \right) + \left( { - \frac{1}{3} + 1} \right) = 0\)

\(\left( {\frac{1}{2} - \frac{2}{3} - 1} \right)x + \frac{2}{3} = 0\)

\(\frac{{ - 7}}{6}x + \frac{2}{3} = 0\)

\(\frac{{ - 7}}{6}x =  - \frac{2}{3}\)

\(x =  - \frac{2}{3}:\frac{{ - 7}}{6}\)

\(x =  - \frac{2}{3} \cdot \frac{6}{{ - 7}}\)

\(x = \frac{4}{7}\)

Vậy \(x = \frac{4}{7}.\)