Elementary Geometry for College Students (7th Edition)

Published by Cengage
ISBN 10: 978-1-337-61408-5
ISBN 13: 978-1-33761-408-5

Chapter 11 - Section 11.2 - The Cosine Ratio and Applications - Exercises - Page 512: 39a


angle A = 68°

Work Step by Step

Let take angle A as α in parallelogram ABCD therefore cos α = $\frac{length of adjacent}{length of hypotenuse}$ cos α = $\frac{10 - 7}{8}$ = $\frac{3}{8}$ therefore α = $cos^{-1}$($\frac{3}{8}$) = 68° so angle A = 68°
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