Answer
m$\angle$A=40$^{\circ}$
Work Step by Step
m$\angle$ABR=m$\angle$A
m$\angle$ABR+m$\angle$A+m$\angle$ARB=180
2m$\angle$A+100=180
m$\angle$A=40$^{\circ}$
Elementary Geometry for College Students (5th Edition)
by Alexander, Daniel C.; Koeberlein, Geralyn M.
Published by
Brooks Cole
ISBN 10:
1439047901
ISBN 13:
978-1-43904-790-3
Chapter 3 - Section 3.3 - Isosceles Triangles - Exercises - Page 153: 39c
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