0 \\
t^2-8*t-9=0 \\
D=64+36=100=10^2 \\
t_1=(8-10)/2=-1 <0 \\
t_2=(8+10)/2=9\\
3^x=9 \\
x=2
" alt="9^x-8*3^x-9=0 \\
3^{2x}-8*3^x-9=0 \\
t=3^x, t>0 \\
t^2-8*t-9=0 \\
D=64+36=100=10^2 \\
t_1=(8-10)/2=-1 <0 \\
t_2=(8+10)/2=9\\
3^x=9 \\
x=2
" align="absmiddle" class="latex-formula">
Ответ: 2.