\(S=1+3+3^2+3^3+...+3^{2019}\)
\(\Rightarrow3S=3+3^2+3^3+3^4+...+3^{2020}\)
\(\Rightarrow3S-S=2^{2020}-1\)
\(\Rightarrow S=\frac{2^{2020}-1}{2}\)
A = 1+3+32+33+......+32019
3A = 3 + 32+33+......+32019 + 32020
2A = (3 + 32+33+......+32019 + 32020) - (1+3+32+33+......+32019)
2A = 32020-1
=> A = 32020-1/2
Vậy...