Tìm x, biết: a) x - 5/6 = - 7/6

a) \(x - \frac{5}{6} = \frac{{ - 7}}{6}\)

\(x = \frac{{ - 7}}{6} + \frac{5}{6}\)

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

\(x = \frac{{ - 1}}{3}.\)

Vậy \(x = \frac{{ - 1}}{3}.\)

b) \[x + 1,05 = 0,2 - 4,25\]

\[x + 1,05 =  - 4,05\]

\[x =  - 4,05 - 1,05\]

\[x =  - 5,1\].

Vậy \[x =  - 5,1.\]

c) \(\left( {5 - 4x} \right)\left( {\frac{5}{4}x - 2} \right) = 0\)

\[5 - 4x = 0\] hoặc \(\frac{5}{4}x - 2 = 0\)

Trường hợp 1:

\[5 - 4x = 0\]

\(4x = 5\)

\(x = \frac{5}{4}\)

Trường hợp 2:

\(\frac{5}{4}x - 2 = 0\)

\(\frac{5}{4}x = 2\)

\(x = 2:\frac{5}{4}\)

\(x = \frac{8}{5}.\)Vậy \(x \in \left\{ {\frac{5}{4};\,\,\frac{8}{5}} \right\}.\)