Giải thích các bước giải:
Sửa đề:
`B = 1/1.5 + 1/5.9 +...+ 1/2018.2022`
`= 1/4 . (4/1.5 + 4/5.9 +...+ 4/2018.2022)`
`= 1/4 . (1 - 1/5 + 1/5 - 1/9 +...+ 1/2018 - 1/2022)`
`= 1/4 . (1 - 1/2022)`
`= 1/4 . 2021/2022 = 2021/8088`
`C= 1/10.12 + 1/12.14 +...+ 1/998.1000`
`= 1/2 . (2/10.12 + 2/12.14 +...+ 2/998.1000)`
`= 1/2 . (1/10 - 1/12 + 1/12 - 1/14 +...+ 1/998 - 1/1000)`
`= 1/2 . (1/10 - 1/1000)`
`= 1/2 . 99/1000 = 99/2000`