Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 6 - Section 6.2 - Trigonometry of Right Triangles - 6.2 Exercises - Page 488: 41

Answer

$\angle A=\dfrac{3\pi}{8}$ $a\approx30.95$ $;$ $b\approx12.82$

Work Step by Step

The triangle is shown in the attached image below. Two angles of the triangle are known. Let the unknown angle be $\angle A$, $\angle B$ be the angle marked as $\dfrac{\pi}{8}$ and $\angle C$ be the right angle. Since $\angle A+\angle B+\angle C=\pi$, substitute the known angles into the formula and solve for $\angle A$: $\angle A=\pi-\dfrac{\pi}{2}-\dfrac{\pi}{8}=\dfrac{3\pi}{8}$ Use the cosine trigonometric ratio of the angle marked as $\dfrac{\pi}{8}$ to obtain the unknown cathetus marked as $a$: $\cos\dfrac{\pi}{8}=\dfrac{a}{33.5}$ $a=33.5\cos\dfrac{\pi}{8}\approx30.95$ Use the Pythagorean Theorem to obtain the other cathetus $b$: $b=\sqrt{33.5^{2}-30.95^{2}}\approx12.82$
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