`A = 1/2 - 1/2^4 + 1/2^7 - 1/2^10 +....+1/2^55 - 1/2^58`
`2^3A = 1/2^4 - 1/2^7 + 1/2^10 -....-1/2^55 + 1/2^58 - 1/2^59`
`8A+A=(1/2^4 - 1/2^7 + 1/2^10 -....-1/2^55 + 1/2^58 - 1/2^59) + (1/2 - 1/2^4 + 1/2^7 - 1/2^10 +....+1/2^55 - 1/2^58)`
`9A = -1/2^59 + 1/2`
`A = (-1/2^59 + 1/2)/9`
(Chúc bạn học tốt)