Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 2 - Section 2.5 - Cardinality of Sets - Exercises - Page 177: 30

Answer

The set of all whole numbers (i.e. integers) is countable. Hence, the set of all three-tuples in $(a,b,c)$ is countable too

Work Step by Step

All whole numbers (i.e. integers) is countable. Hence, the set of all three-tuples in $(a,b,c)$ is countable too so that we can list all three tuples: so equation whose coefficients are formed by {$a(j),b(j),c(j)$},$ j$ runs from $1$ to infinity, there corresponds, in general, at most $2$ real roots $x$ and $ y$. Mark them as $x_{1}$ and $y_{j}$. Then we have a set of pairs {$x_{1}, y_{1}$} {$x_{2}, $y_{2}$}.... which is countable.
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