Question

Chứng minh: 7^1+7^2+7^3+...+7^117+7^118 chia hết cho 57

Answer 1

\(=7\left(1+7+7^2\right)+...+7^{115}\left(1+7+7^2\right)+118\)

\(=57\left(7+...+7^{115}\right)+7^{118}⋮57\)