Question

 Cho: A = 3 + 3² + 3³ + ..... + 3³⁰
Chứng minh: A ⋮ 13
                      A ⋮ 52

Answer 1

\(A=3\left(1+3+3^2\right)+...+3^{28}\left(1+3+3^2\right)\)

\(=13\left(3+...+3^{28}\right)⋮13\)

Answer 2

x∈{−1;−3;0;−4;1;−5;4;−8}