1 câu trả lời
`25^2021 + 8` chia hết cho` 11`.
Ta có: `25^1 ≡ 3 (mod 11)`
`25^2 ≡ 9 (mod 11)`
`25^3 ≡ 5 (mod 11)`
`25^4 ≡ 4 (mod 11)`
`25^5 ≡ 3 (mod 11)`
`=> 25^2021 + 8 = (25^4)^505 . 5 +8 `
Ta có:`( 25^4 ) ^505 .5 ≡3 ( mod 11 )`
`8 ≡ 8 (mod 11)`
=> `25^2021 + 8 ≡ 3 + 8 =11 vdots 11`
#AC
