\(A=2+2^2+2^3+...+2^{60}\)
\(\Leftrightarrow2A=2^2+2^3+2^4+...+2^{61}\)
\(\Leftrightarrow2A-A=2^{61}-2\)
\(\Leftrightarrow A+2=2^{61}-2+2\)
\(\Leftrightarrow A+2=2^{61}\left(đpcm\right)\)
a) Ta có: \(A=2+2^2+2^3+...+2^{60}\)
\(\Rightarrow A+2=2+2+2^2+2^3+...+2^{60}\)
\(\Rightarrow2.\left(A+2\right)=2.\left(4+2^2+2^3+...+2^{60}\right)\)
\(\Rightarrow2A+4=8+2^3+...+2^{61}\)
\(\Rightarrow2A+4-\left(A+2\right)=8+2^{61}-\left(4+2^2\right)=2^{61}+8-8=2^{61}\)
\(\Rightarrow A+2=2^{61}\)
(Câu b bạn cứ tính 2B + 3 bình thường, sau đó làm tương tự nhé)
\(B=3+3^2+3^3+...+3^{40}\)
\(\Leftrightarrow3B=3^2+3^3+3^4+...+3^{40}\)
\(\Leftrightarrow2B=3^{41}-3\)
\(\Leftrightarrow2B+3=3^{41}-3+3\)
\(\Leftrightarrow2B+3=3^{41}\left(đpcm\right)\)