Răspuns:
[tex] {9}^{x} + 2 \times {3}^{x} = 99[/tex]
[tex] {( {3}^{2} )}^{x} + 2 \times {3}^{x} = 99 \\ {( {3}^{x} ) }^{2} + 2 \times {3}^{x} = 99 \\ {t}^{2} + 2t = 99 \\ t = - 11 \\ t = 9 \\ {3}^{x} = - 11 \\ {3}^{x} = 9 \\ x \: nu \: apartine \: multimii \: nr \: naturale \\ x = 2[/tex]
