`A = 1 + 1/8 + 1/24 + 1/80 + 1/120`
`A = 1 + 1/(2.4) + 1/(4.6) + 1/(8.10) + 1/(10.12)`
`2A = 2 + 2/(2.4) + 2/(4.6) + 2/(8.10) + 2/(10.12)`
`2A = 2 + 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + 1/8 - 1/10 + 1/10 - 1/12`
`2A = 2 + 1/2 - 1/12`
`2A = 24/12 + 6/12 - 1/12`
`2A = (24+6-1)/12`
`2A = 29/12`
`A = 29/12 : 2`
`A = 29/12 xx 1/2`
`A = 29/(12xx2)`
`A = 29/24`
Vậy `A=29/24`
