Tìm (x), biết:

a) \(2 + x:5 = 6\)

\(x:5 = 4\)

\(x = 20\)

Vậy \(x = 20\).

b) \(51 - 3\left( {x + 2} \right) = 60\)

\(3\left( {x + 2} \right) = 51 - 60\)

\(3\left( {x + 2} \right) =  - 9\)

\(x + 2 =  - 3\)

\(x =  - 5\)

Vậy \(x =  - 5\).

c) \({2^x} + {2^{x + 3}} = 144\)

\({2^x} + {2^x}{.2^3} = 144\)

\({2^x}.\left( {1 + {2^3}} \right) = 144\)

\({2^x}.9 = 144\)

\({2^x} = 16\)

\({2^x} = {2^4}\)

Suy ra \(x = 4\).

Vậy \(x = 4\).