Unformatted text preview: set of positive even integers E is a countable set. Solution: let f (x) = 2x. Z+: 1 2 3 4 5 6 … 2 4 6 8 10 12 … Then f is a bijection from Z+ to E since f is both one to one and onto. Posi$ve Ra$onal Numbers are Countable ༉ Reminder: a rational number can be expressed as the ratio of two integers p and q such that q ≠ 0. ༉ 3/4 is a rational number. ༉ √2 is not a rational number. Example 2: show that the positive rational numbers are countable. Solution: the positive rational numbers are countable since they can be arranged in a sequence: r1 , r2 , r3 , … The next slide shows how this is done. → Posi$ve Ra$onal Numbers are Countable First row q = 1. Second row q = 2. etc. Constructing the List First list p/q with p + q = 2. Second list p/q with p + q = 3 Third list p/q with p + q = 4, and so on. Matrices ༉ Matrices are useful discrete structures that can be used in many ways. For example, they are used to: ༉ Describe certain types of functions known as linear transformations , e.g., they are used in computer graphics. ༉ Express which vertices of a graph are connected by edges. ༉ Later, we will see...
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This document was uploaded on 02/27/2014 for the course CS 215 at SIU Carbondale.
 Spring '14
 M.Nojoumian
 Computer Science

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