Question

7³+7⁴+7⁵chia het cho 57

Answer 1

7^3 + 7^4 + 7^5

= 7^3 . 1 + 7^3 . 7^1 + 7^3 . 7^2

= 7^3 . 1 + 7^3 . 7 + 7^3 . 49

= 7^3 . (1+7+49)

= 7^3 . 57 chia hết cho 57

Vậy 7^3 + 7^4 + 7^5 chia hết cho 57

Answer 2

\(7^3+7^4+7^5=7^3+7^3.7+7^3.7^2=7^3.\left(1+7+49\right)=7^3.57⋮57\)