[tex]\it S=1+3+3^2+3^3+\ ...\ +3^{79}+3^{80}\\ \\ 3S=3+3^2+3^3+...\ +3^{80}+3^{81}\\ \\ 3S-S=3^{81}-1 \Rightarrow 2S = 3^{81}-1\\ \\ 2S>27^{27}-9 \Rightarrow 3^{81}-1>(3^3)^{27}-9 \Rightarrow 3^{81}-1>3^{81} -9\Rightarrow \\ \\ \Rightarrow -1+9>3^{81}-3^{81} \Rightarrow 8>0\ \ (A)[/tex]
