Question

aratati ca nr 3+3^2+3^3+.....+3^123 se divide cu 13

Answer 1

[tex]a=3+3^2+3^3+...+3^{123}\\ a=3(1+3+3^2)+....+3^{121}(1+3+2^2)\\ a=(1+3+3^2)(3+3^4+....+3^{121})\\ a=13(3+3^4+...+3^{121})[/tex]