Cứu tui câu này vs mấy ní ơi

Đặt `A = 2018/1+ 2017/2 + 2016/3 +.....+1/2018`

       `A= (1+1+1+...+1) + 2017/2 + 2016/3 +.....+1/2018`

       `A = (1+2017/2)+(1+2016/3) +....+(1+1/2018) + 1`

       `A = 2019/2 + 2019/3 +....+2019/2018 +2019/2019`

       `A = 2019 . (1/2 + 1/3 +....+1/2019)`

`⇒ D = (2018/2 + 2018/3 +.....+2018/2019) /(2019 . (1/2 + 1/3 +....+1/2019))`

`⇒ D = (2018.(1/2+1/3+....+1/2019))/(2019 . (1/2 + 1/3 +....+1/2019))`

`⇒ D = 2018/2019`

   Vậy `D = 2018/2019`