Question

 Cho A = 1+ 2+2^2+2^3 + ......+ 2^ 50

tính A

Answer 1

\(\Rightarrow2A=2+2^2+2^3+2^4+...+2^{51}.\)

\(\Rightarrow2A-A=A=\left(2+2^2+2^3+2^4+...+2^{51}\right)-\left(1+2^2+2^3+...+2^{50}\right)\)

\(A=2^{51}-1\)

Answer 2

\(A=1+2+2^2+2^3+....+2^{50}\)

\(\Rightarrow2A=2+2^2+2^3+2^4+...+2^{51}\)

\(\Rightarrow2A-A=(2+2^2+2^3+2^4+...+2^{51})\)_\((1+2^2+2^3+...+2^{50})\)

Hay \(A=2^{51}-1\)