Elementary Linear Algebra 7th Edition

Published by Cengage Learning
ISBN 10: 1-13311-087-8
ISBN 13: 978-1-13311-087-3

Chapter 5 - Inner Product Spaces - Review Exercises - Page 284: 14



Work Step by Step

$$\| c(2,2,-1)\|=3\Longrightarrow |\|c (2,2,-1)\|^2=9 \Longrightarrow c^2 (4+4+1)=9$$ then, we get $c^2=1$ and hence $$c=-\pm1.$$
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