[tex] 3^{x+1} + 3^{x-1} \ \textless \ 28[/tex]

3^(x+1)+3^(x-1)<289*3^(x-1)+3^(x-1)<28(9+1)*3^(x-1)<283^(x-1)<28/103^(x-1)<14/5x-1 < log(3, 14/5)x < 1 + log(3, 14/5)x < log(3, 42/5)