Elementary Geometry for College Students (6th Edition)

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

Chapter 2 - Section 2.4 - The Angles of a Triangle - Exercises - Page 92: 4


$m∠A=m\angle C =69^{\circ}$

Work Step by Step

we know sum of all three angles of triangle is $180^{\circ}$ $m∠A+m∠B+m∠C$=$180^{\circ}$ $m\angle A+42^{\circ}+m\angle C$ = $180^{\circ}$ $m∠A+m\angle C $= $180^{\circ}−42^{\circ}$ $m∠A+m\angle C $ = $138^{\circ}$ $m∠A=m\angle C= 138^{\circ}\div2 =69^{\circ}$
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