Intermediate Algebra for College Students (7th Edition)

Published by Pearson
ISBN 10: 0-13417-894-7
ISBN 13: 978-0-13417-894-3

Chapter 4 - Section 4.2 - Compound Inequalities - Concept and Vocabulary Check - Page 272: 3



Work Step by Step

The set of elements both in $(-\infty,9)$ and $(-\infty,12)$ is $(-\infty,9)$ because the first set is all elements less than $9$ and the second set is all elements less than $12$. Thus if something is in both, then it is less than $9$ and $12$, but $12\gt9$, so this is equivalent to something being less than $9$.
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