Chapter 3 - Solving Inequalities - 3-8 Unions and Intersections of Sets - Practice and Problem-Solving Exercises - Page 220: 41

$A \times B$ = {$(\pi, 2), (\pi, 4), (2\pi, 2), (2\pi, 4), (3\pi, 2), (3\pi, 4), (4\pi, 2), (4\pi, 4)$}

We are asked to give the cross products of two sets $A$ and $B$. This means we have to come up with ordered pairs that have the first element of the ordered pair in $A$ and the second element of the ordered pair in $B$. $A \times B$ = {$(\pi, 2), (\pi, 4), (2\pi, 2), (2\pi, 4), (3\pi, 2), (3\pi, 4), (4\pi, 2), (4\pi, 4)$}