What universal set $(U)$ would you propose for the set of right triangles?

Write the following set in the set-builder form: $\{ 1, 4, 9, \ldots, 100 \}$

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

Write the following interval in set-builder form: $\left[ -23, 5 \right)$

If $aN = \{ ax : x \in N \}$,then the set $3N \cap 7N$ is equal to $kN$,where $k$ is:

Which of the following pairs of sets are equal? Justify your answer.
$A = \{ n : n \in \mathbb{Z} \text{ and } n^2 \le 4 \}$ and $B = \{ x : x \in \mathbb{R} \text{ and } x^2 - 3x + 2 = 0 \}$.