Tìm (x), biết:

a) \(678 + \left( {x - 218} \right) = 541\)

\(x - 218 = 541 - 678\)

\(x - 218 =  - 137\)

\(x =  - 137 + 218\)

\(x = 81\)

Vậy \(x = 81\).

b) \(3\left( {x + 2} \right) - 11 =  - 2\)

\(3\left( {x + 2} \right) = -2 + 11\)

\(3\left( {x + 2} \right) = 9\)

\(x + 2 = 3\)

\(x = 1\)

Vậy \(x = 1\).

c) \({5.3^{x - 1}} + {3^{x - 1}} = 162\)

\[{3^{x - 1}}.\left( {5 + 1} \right) = 162\]

\[{3^{x - 1}}.6 = 162\]

\[{3^{x - 1}} = 162 : 6\]

\[{3^{x - 1}} = 27\]

\({3^{x - 1}} = {3^3}\)

Suy ra \(x - 1 = 3\)

  \(x = 4\)

Vậy \(x = 4\).