Question

A=x|x apartine N ,9 <3la puterea x <81

Answer 1

$9 \ \textless \ 3^{n} \ \textless \ 81$
$3^{2} \ \textless \ 3^{n} \ \textless \ 3^{4}$
2 < n < 4
n ∈ N ⇒ n= 3