Intermediate Algebra (6th Edition)

Published by Pearson
ISBN 10: 0321785045
ISBN 13: 978-0-32178-504-6

Chapter 3 - Section 3.5 - Equations of Lines - Exercise Set - Page 174: 89



Work Step by Step

A vertical line is always perpendicular to a horizontal line. This cannot be justified, though, by algebra and the use of slopes. This is because a horizontal line has a slope of $0$ while a vertical line has an undefined slope. These two slopes are not negative reciprocals of each other. The justification, instead, uses geometry and angles.
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