[tex]2 \times 10^n + 70 = 2\underbrace{000 \hdots 000} + 70 = 2\underbrace{000 \hdots 070} \\
.~~~~~~~~~~~~~~~~~~~~~~~n~zerouri \\
Suma~cifrelor = 2 +0+0+0+ \dots +0+7+0 = \boxed{9} \\
\Longrightarrow ~~(2 \times 10^n + 70 ) ~\vdots ~9 \\
Cazuri ~particulare: \\
n=0 ~\Rightarrow~2 \times 10^0 + 70 =2 \times 1 + 70 =2+70=72~\vdots ~9 \\
n=1 ~\Rightarrow~2 \times 10^1 + 70 =2 \times 10 + 70 =20+70=90~\vdots ~9 \\
n=2 ~\Rightarrow~2 \times 10^2 + 70 =2 \times 100 + 70 =200+70=270~\vdots ~9 \\
etc.[/tex]
