Tính các tổng sau:

Question

B=1+1/2+1/4+...+1/2^100

Answer 1

Từ B suy ra 2B=2+1+1/2+...+1/2^99.

=> 2B-B=(2+1+1/2+...+1/2^99)-(1+1/2+1/4+...+1/2^100)

             =2 - 1/2^100.

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