Sửa lại đề: `129/66 to 129/64`

Ta có

`A = 5/2 + 9/4 + 17/8 + 33/16 + 65/32 + 129/64 + 257/128 + 513/256 + 1025/512 + 2047/1024`

`A = (2+1/2) + (2+1/4) +(2+1/8) + (2+1/16) + (2+1/32) + (2+1/64) + (2+1/128) + (2+1/256) + (2+1/512) + (2+1/1024)`

`A= (2 xx 10) + (1/2 + 1/4 + 1/8+1/16 + 1/32+1/64+1/128 + 1/256 + 1/512 + 1/1024)`

`A = 20 + (1-1/1024)`

`A = 20 + 1023/1024`

`A = 21503/1024`