Đáp án `+` Giải thích các bước giải:

`A = 1/2 + 1/4 + 1/8 + 1/16 + ... + 1/1024`

`2A = 1 + 1/2 + 1/4 + 1/8 + ... + 1/512`

`2A - A = (1 + 1/2 + 1/4 + 1/8 + ... + 1/512) - (1/2 + 1/4 + 1/8 + 1/16 + ... + 1/1024)`

`A = 1 - 1/1024`

`A = 1023/1024`

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`B = 1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729`

`3B = 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243`

`3B - B = (1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243) - (1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729)`

`2B = 1 - 1/729 = 728/729`

`B = 364/729`

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`C = 1/5 + 1/10 + 1/20 + 1/40 + 1/80 + 1/160 + 1/320`

`2C = 2/5 + 1/5 + 1/10 + 1/20 + 1/40 + 1/80 + 1/160`

`2C - C = (2/5 + 1/5 + 1/10 + 1/20 + 1/40 + 1/80 + 1/160) - (1/5 + 1/10 + 1/20 + 1/40 + 1/80 + 1/160 + 1/320)`

`C = 2/5  - 1/320`

`C = 127/320`

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`D = 3/2 + 3/8 + 3/32 + 3/128 + 3/512`

`1/3D = 1/2 + 1/8 + 1/32 + 1/128 + 1/512`

`4/3D = 2 + 1/2 + 1/8 + 1/32 + 1/128`

`4/3D - 1/3D = (2 + 1/2 + 1/8 + 1/32 + 1/128) - (1/2 + 1/8 + 1/32 + 1/128 + 1/512)`

`D = 2 - 1/512`

`D = 1023/512`

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`E = 5/2 + 5/6 + 5/18 + 5/54 + 5/162 + 5/486`

`1/5E = 1/2 + 1/6 + 1/18 + 1/54 + 1/162 + 1/486`

`3/5E = 3/2 + 1/2 + 1/6 + 1/18 + 1/54 + 1/162`

`3/5E - 1/5E = (3/2 + 1/2 + 1/6 + 1/18 + 1/54 + 1/162) - (1/2 + 1/6 + 1/18 + 1/54 + 1/162 + 1/486)`

`2/5E = 3/2 - 1/486`

`2/5E = 364/243`

`E = 364/243 . 5/2`

`E = 910/243`

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