Elementary Geometry for College Students (6th Edition)

Published by Brooks Cole
ISBN 10: 9781285195698
ISBN 13: 978-1-28519-569-8

Chapter 1 - Section 1.2 - Informal Geometry and Measurement - Exercises - Page 17: 2


Angle ABC is smaller than DEF. ABC is an acute angle while DEF is an obtuse angle.

Work Step by Step

First, look at both angles. You will see that ABC has a narrower opening than DEF, meaning it is a smaller angle (the angle ABC will measure fewer degrees than DEF). Also, intuitively, you can see that angle ABC is narrower than the angle of a standard piece of paper (which is a right angle, also known as a 90$^{\circ}$ angle), which means it is an acute angle. DEF is wider than the angle of a piece of paper, so it is an obtuse angle.
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