A=1/2+1/4+1/8+...+1/2056

2 câu trả lời

`A=1/2+1/4+1/8+...+1/2056`

`=>2A=1+1/2+1/4+1/8+...+1/1025`

`=> 2A-A=(1+1/2+1/4+1/8+...+1/1025)-(1/2+1/4+1/8+...+1/2056)`

`=>A=1-1/2056`

`=>A=2055/2056`

Vậy `A=2055/2056`

Ax2-A=(1+1/2+1/4+...+1/1028)-(1/2+1/4+1/8+...+1/2056) A=1-1/2056=2055/2056

Đáp số : 2055/2056

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