Tìm x, biết: 3^(x + 1) + (3^x).5 = 216

\[{3^{x + 1}} + {3^x}.5 = 216\]

\[{3^x}.3 + {3^x}.5 = 216\]

\[{3^x}.\left( {3 + 5} \right) = 216\]

\[{3^x}.8{\rm{ }} = 216\]

\[{3^x} = {\rm{ }}216:{\rm{ }}8\]

\[{3^x} = 27\]

\[{3^x} = {\rm{ }}{3^3}\]

\[x{\rm{ }} = 3\]