Đáp án:
Giải thích các bước giải:
Câu 1 :
`A =` $\dfrac{2018.2019 + 1}{2018.2019}$
`=` $\dfrac{2018.2019}{2018.2019}$ `+` $\dfrac{1}{2018.2019}$
`= 1 +` $\dfrac{1}{2018.2019}$
Tương tự:
`B =` $\dfrac{2019.2020 + 1}{2019.2020}$.
`= 1 +` $\dfrac{1}{2019.2020}$
Do: `1 +` $\dfrac{1}{2018.2019}$ `> 1 +` $\dfrac{1}{2019.2020}$
Vậy A > B
Câu 2 :
`S = 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/2018.2019`
`= 1 - 1/2 + 1/2 + 1/3 + 1/3 - 1/4 + ... + 1/2018 - 1/2019`
`= 1 - 1/2019`
`= 2019/2019 - 1/2019`
`= 2018/2019`
Mà `2018/2019 < 1`
`S = 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/2018.2019 < 1`