11/15 + 11/35 + 11/63 + 11/99

Đáp án + Giải thích các bước giải:

    `11/15 + 11/35 + 11/63 + 11/99`

`= 11 × (1/15 + 1/35 + 1/63 + 1/99)`

`= 11/2 × 2 × (1/15 + 1/35 + 1/63 + 1/99)`

`= 11/2 × (2/(3 × 5) + 2/(5 × 7) + 2/(7 × 9) + 2/(9 × 11))`

`= 11/2 × (1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11)`

`= 11/2 × (1/3 - 1/11)`

`= 11/2 × (11/33 - 3/33)`

`= 11/2 × 8/33`

`= 4/3`

#DeariaChira!