Answer
$A\times B=\{(\pi,2),(\pi,4),(2\pi,2),(2\pi,4),(3\pi,2),(3\pi,4),(4\pi,2),(4\pi,4)\}$
Work Step by Step
$A\times B$ is a set of ordered pairs, where each element of A is mapped to each element of B. The element from A appears as the first element in the ordered pair.
$\ \ \pi\rightarrow\ \ |\overset\rightarrow\ 2$
$\ \ \ \ \,\ \ \ \ \ \ \ \ |\overset\rightarrow\ 4$
$2\pi\rightarrow\ \ |\overset\rightarrow\ 2$
$\ \ \,\ \ \ \ \ \ \ \ \ \ |\overset\rightarrow\ 4$
$3\pi\rightarrow\ \ |\overset\rightarrow\ 2$
$\ \ \,\ \ \ \ \ \ \ \ \ \ |\overset\rightarrow\ 4$
$4\pi\rightarrow\ \ |\overset\rightarrow\ 2$
$\ \ \,\ \ \ \ \ \ \ \ \ \ |\overset\rightarrow\ 4$
