A=(1+1/3).(1+1/8).(1+1/15).....(1+1/624).Tính a

Đáp án:

 `A = =25/13`

Giải thích các bước giải:

`A=(1+1/3)(1+1/8)(1+1/15)...(1+1/624)`

`=4/{3}.{9}/{8}.{16}/{15}...{625}/624`

`={2^2}/{1.3}.{3^2}/{2.4}.{4^2}/{3.5}...{25^2}/{24.26}`

`={2^{2}.3^{2}.4^{2}...25^2}/{1.3.2.4.3.5...24.26}`

`={(2.3.4...25)(2.3.4...25)}/{(1.2.3...24)(3.4.5...26)}`

`={25.2}/{26}`

`=50/26`

`=25/13`