(1,5 điểm) Tìm x , biết: a) 5 x − 2 3 = 3 3 .b) 51 − 3 ( x + 2 ) = 60 ;c) 3 x + 2 + 3 x = 10 .

a) \(5x - {2^3} = {3^3}\)

\(5x - 8 = 27\)

\(5x = 35\)

\(x = 7\)

Vậy \(x = 7\).

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) \({3^{x + 2}} + {3^x} = 10\)

\({3^x}{.3^2} + {3^x} = 10\)

\({3^x}.\left( {{3^2} + 1} \right) = 10\)

\({3^x}.10 = 10\)

\({3^x} = 1\)

\({3^x} = {3^0}\)

Suy ra \(x = 0\).

Vậy \(x = 0\).