Question

Dem. ca A=1+2+2^2+2^3+...+2^98 divizibil cu 7

Answer 1

[tex]A=(1+2+2^2)+2^3(1+2+2^2)+...+2^{96}(1+2+2^2)\\ A=7+7\cdot2^3+...+7\cdot 2^{96}\\ A=7\cdot(1+2^3+...+2^{96})\\ A\vdots7[/tex]