Question

1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128

Answer 1

Gọi tổng này là A

<=> 2A = 1 + 1/2 + 1/4 + ... + 1/64

=> 2A - A = ( 1 + 1/2 + 1/4 + ... + 1/64 ) - ( 1/2 + 1/4 + 1/8 + ... + 1/128 )

         A      = 1 - 1/128

         A      = 127/128

Ủng hộ ae ơiii

Answer 2

Bằng 127/128

Answer 3

\(\text{Đặt A}=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{128}\)

\(\Rightarrow2A=1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{64}\)

\(\Rightarrow A=\left(1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{64}\right)-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{128}\right)\)

\(=1-\frac{1}{128}\)

\(=\frac{127}{128}\)