Tính : c, 1+`1/8`+`1/24`+`1/48`+`1/80`+`1/120`+`1/168`

Giải thích các bước giải:

`c)`

`Đặt  A = 1 + 1/8 + 1/24 + 1/48 + 1/80 + 1/120 + 1/168`

`A = 1 + 1/(2 . 4) + 1/(4 . 6) + 1/(6 . 8) + 1/(8 . 10) + 1/(10 . 12) + 1/(12 . 14)`

`2A = 2 + (2/(2 . 4) + 2/(4 . 6) + 2/(6 . 8) + 2/(8 . 10) + 2/(10 . 12) + 2/(12 . 14))`

`2A = 2 + (1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + 1/8 - 1/10 + 1/10 - 1/12 + 1/12 - 1/14)`

`2A = 2 + (1/2 - 1/14)`

`2A = 2 + 3/7`

`2A = 17/7`

`A = 17/14`