Đáp án + Giải thích các bước giải:
6a)
`1/1.2+1/2.3+1/3.4+...+1/99.100`
`=1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100`
`=1-1/100=100/100-1/100=99/100`
6b)
`2/3.5+2/5.7+2/7.9+2/9.11+...+2/99.101`
`=1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+...+1/99-1/101`
`=1/3-1/101=101/303-3/303=98/303`
7a)
`2020/2021=2021/2021-1/2021=1-1/2021`
`2022/2023=2023/2023-1/2023=1-1/2023`
Vì `1/2021>1/2023`
`=>1-1/2021<1-1/2023`
Vậy `2020/2021<2022/2023`
7b)
`71/70=70/70+1/70=1+1/70`
`69/68=68/68+1/68=1+1/68`
Vì `1/68>1/70`
`=>1+1/68>1+1/70`
Vậy `69/68>71/70`
