The fundamental counting rule
This section is devoted to counting the number of possible ways to select several objects, each from a set of distinct elements. We will first focus on the case of just two sets before extending it to an arbitrary number of sets.
Definition – the Cartesian product
The set of ordered pairs A × B = {(a, b) : a A, b
B}, with component a as an element from set A and the second component b from set B, is called the Cartesian product of sets A and B:
Figure 4.1 – If A = {a1, a2} and B = {b1, b2}, then A × B consists of the ordered pairs in this table
This chapter is all about counting the number of elements in sets. Recall from Chapter 1, Key Concepts, Notation, Set Theory, Relations, and Functions that the cardinality of a set is the number of elements in the set. Cartesian products are interesting things to count because we can count the number of ways of choosing one element from set A and another element...