Question

demonstrati ca 9 la n -1 se divide cu 8

Answer 1

$\it 9^n-1=9^n-1^n=(9-1)(9^{n-1}+9^{n-2}+9^{n-3}+\ ...\ +9+1)=\\ \\ 8\cdot(9^{n-1}+9^{n-2}+9^{n-3}+\ ...\ +9+1)\in M_{8},\ \forall\ n\in\mathbb{N}$

Answer 2

........................................