Question

bài khó quá bạn nào là được thì giúp mình 

 

Answer 1

\(2A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{2021}}\)

\(2A-A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{2021}}-\dfrac{1}{2}-\dfrac{1}{2^2}-...-\dfrac{1}{2^{2022}}=1-\dfrac{1}{2^{2022}}=\dfrac{2^{2022}-1}{2^{2022}}\)

Answer 2

\(\Rightarrow2A=1+\dfrac{1}{2}+....+\dfrac{1}{2^{2021}}\)

\(\Rightarrow2A-A=1+\dfrac{1}{2}+....+\dfrac{1}{2^{2021}}-\dfrac{1}{2}-\dfrac{1}{2^2}-...-\dfrac{1}{2^{2022}}\)

\(\Rightarrow A=1-\dfrac{1}{2^{2022}}\)