Đáp án:
Giải thích các bước giải:
`3)`
`A = 4 + 4^2 + 4^3 +.......+ 4^202`
`-> 4A = 4^2 + 4^3 + 4^4 +......+ 4^203`
`-> 4A - A = 4^203 - 4`
`-> 3A = 4^203 - 4`
`-> A = (4^203 - 4)/3`
`4)`
`2018 . 2018 = 2018 . ( 2017 + 1 ) = 2018 . 2017 + 2018`
`2017 . 2019 = 2017 . ( 2018 + 1 ) = 2017 . 2018 + 2017`
-Ta có: `2018 > 2017`
`-> 2018 . 2017 + 2018 > 2018 . 2017 + 2017`
`-> 2018 . 2018 > 2017 . 2019`
`#Dung09`