Question

A=1+2¹+2²+2³+...+2²⁰

Giải nhanh hộ mình nha!

Answer 1

\(A=1+2^1+2^2+...+2^{20}\)

\(\Rightarrow2A=2+2^2+2^3+...+2^{21}\)

\(\Rightarrow2A-A=\left(2+2^2+2^3+...+2^{21}\right)-\left(1+2^1+2^2+...+2^{20}\right)\)

\(\Rightarrow A=2^{21}-1\)

Chúc bạn học tốt!

Answer 2

\(A=1+2^1+2^2+2^3+...+2^{20}\)

=> \(2A=2+2^2+2^3+2^4+...+20^{21}\)

=> \(2A-A=\left(2+2^2+2^3+2^4+...+2^{21}\right)-\left(1+2^1+2^2+2^3+...2^{20}\right)\)

=> \(A=2^{21}-1\)