Помогите!!!!

$9^x+3 ^{x+1} \ \textgreater \ 108$
$3 ^{2x} +3*3^x-108\ \textgreater \ 0$
$3^x=a$
a²+3a-108>0
a1+a2=-3 U a1*a2=-108
a1=-12 U a2=9
a<-12⇒<img src="https://tex.z-dn.net/?f=3%5Ex%5C+%5Ctextless+%5C+-12" id="TexFormula5" title="3^x\ \textless \ -12" alt="3^x\ \textless \ -12" align="absmiddle" class="latex-formula"> нет решения
a>9⇒ $3^x\ \textgreater \ 9$ ⇒x>2
x∈(2;∞)