\(A=1+2+2^2+...+2^{100}\)
\(\Rightarrow2A=2+2^2+2^3+...+2^{100}+2^{101}\)
\(\Rightarrow2A-A=\left(2+2^2+2^3+...+2^{100}+2^{101}\right)-\left(1+2+...+2^{100}\right)\)
\(\Rightarrow A=2^{101}-1\)
\(A=1+2+2^2+2^3+....+2^{100}\\ 2A=2+2^2+2^3+2^4+...+2^{101}\\ 2A-A=2^{101}-1\\ \Rightarrow A=2^{101}-1\\ \)