`9^(x + 1) - 5 . 3^(2x) = 324`
`=> 9^x + 9 - 5 . (3^2)^x = 324`
`=> 9^x + 9 - 5 . 9^x = 324`
`=> 9^x . (9 - 5) = 324`
`=> 9^x . 4 = 324`
`=> 9^x = 324 : 4`
`=> 9^x = 81`
`=>` \(\left[ \begin{array}{l}9^x = 9^2\\9^x = -9^2\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x = 2\\x=-2\end{array} \right.\)
Vậy `x ∈ {2 ; -2}`