Question

1/2 + 1/4 + 1/8 ........ 1/128 + 1/256

Giúp mik 

Answer 1

Đặt tổng là A

\(2xA=1+\dfrac{1}{2}+\dfrac{1}{4}+...+\dfrac{1}{64}+\dfrac{1}{128}\)

\(\Rightarrow A=2xA-A=1-\dfrac{1}{256}=\dfrac{255}{256}\)