Two sets $A$ and $B$ are disjoint if and only if

If ${N_a} = \{an : n \in N\}$,then ${N_3} \cap {N_4} = $

If $A = \{1, 2, 3, 4, 5\}$,then the number of proper subsets of $A$ is

Let $a > 0, a \neq 1$. Then,the set $S$ of all positive real numbers $b$ satisfying $(1+a^2)(1+b^2) = 4ab$ is

In the following,state whether $A=B$ or not:
$A=\{a, b, c, d\} ; B=\{d, c, b, a\}$

Are the following pair of sets equal? Give reasons.
$A = \{ 2, 3 \}, \quad B = \{ x : x \text{ is a solution of } x^2 + 5x + 6 = 0 \}$