Tìm x, biết: a) (123 − 4x) − 67 = 8

a) \[\left( {123 - 4x} \right) - 67 = 8\]

\[123 - 4x = 8 + 64\]

\[123 - 4x = 75\]

\[4x = 123 - 75\]

\[4x = 48\]

\[x = 48:4\]

 \(x = 12\)

Vậy \(x = 12.\)

b) \[\left( {3x - 1} \right) + 18 = - 40\]

    \[3x - 1 = - 40 - 18\]

\[3x - 1 = - 58\]

\[3x =  - 58 + 1\]

\(3x = - 57\)

\(x = - 19.\)

Vậy \(x = - 19.\)

c) \(3 \cdot {\left( {2x - 11} \right)^2} + 6 = {3^4}\)

\(3 \cdot {\left( {2x - 11} \right)^2} = 81 - 6\)

\(3 \cdot {\left( {2x - 11} \right)^2} = 75\)

\({\left( {2x - 11} \right)^2} = 25\)

Trường hợp 1:

\(2x - 11 = 5\)

\(2x = 16\)

\(x = 8\)

Vậy \(x \in \left\{ {3;\,\,8} \right\}.\)

Trường hợp 2:

\(2x - 11 = - 5\)

\(2x = 6\)

\(x = 3\).