Đáp án + Giải thích các bước giải:
a)
`A=3^2020+3^2021+3^2022`
`=>A=3^2020(1+3+3^2)`
`=>A=3^2020 .13\vdots13`
Vậy `A\vdots13`
b)
`A=3^2020+3^2021+3^2022`
`=>A=3^2020(1+3+3^2)`
`=>A=3^2020 .13`
`=>A=3^2018 .3^2 .13`
`=>A=3^2018 .9.13`
`=>A=3^2018 .117\vdots117`
Vậy `A\vdots117`