[tex]\displaystyle \\
\texttt{Vom folosi formula: } \\ \\
n^0+n^1+n^2+ \hdots + n^k = \frac{n^{k+1} - 1}{n-1} \\ \\
\texttt{Rezolvare: } \\ \\
2(1+3+ 3^{2}+...+3^{8} ) =2 \times \frac{3^{8+1} -1}{3-1}= \\ \\
= \frac{2(3^{9} -1)}{2}= \boxed{ 3^{9} -1 \ \textless \ 3^9 } \\ \\ \texttt{cctd}[/tex]
