Sabendo que A × B = {(5, 2), (5, 3), (5, 7), (7, 2), (7, 3), (7, 7), (9, 2) (9, 3) (9, 7)}, o conjunto B é​

\[\left\{ \begin{matrix} A\times B=\{(a_1,b_1),(a_1,b_2),(a_1,b_3),(a_2,b_1),(a_2,b_2),(a_2,b_3),(a_3,b_1),(a_3,b_2),(a_3,b_3)\} \\ B\times A = \{(b_1,a_1),(b_1,a_2),(b_1,a_3),(b_2,a_1),(b_2,a_2),(b_2,a_3),(b_3,a_1),(b_3,a_2),(b_3,a_3) \} \end{matrix} \right.\]

Pelo enunciado, tem-se \(A \times B = \{(5, 2), (5, 3), (5, 7), (7, 2), (7, 3), (7, 7), (9, 2), (9, 3), (9, 7)\}\). Portanto, os elementos dos conjuntos são:

\[\left\{ \begin{matrix} a_1=5 \\ a_2=7 \\ a_3=9 \\ b_1=2 \\ b_2=3 \\ b_3=7 \end{matrix} \right.\]

Portanto, o conjunto \(B\) é igual a \(\boxed{B=\{2,3,7\}}\).