arătați că a =2 la puterea n +1 ori 5 la puterea n +2 la puterea n ori 3 la puterea n+2 se divide cu 11. Plz e urgent. Dau coroana (ps. Doar ex 6)

[tex]\it a=2^{n+1}\cdot3^n+2^n\cdot3^{n+2}=2\cdot2^n\cdot3^n+2^n\cdot3^n\cdot3^2=2\cdot(2\cdot3)^n+(2\cdot3)^n\cdot9=\\ \\ = 2\cdot6^n+6^n\cdot9=6^n(2+9)=6^n\cdot11 \Rightarrow a\ \vdots\ 11[/tex]