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: 43

Answer

$\angle A=\dfrac{3\pi}{10}$ $h\approx180.34$ $;$ $a\approx145.9$

Work Step by Step

The triangle is shown in the attached image below. Two angles are known. Let $\angle A$ be the unknown angle, $\angle B$ be angle marked as $\dfrac{\pi}{5}$ 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 $\angle A$: $\angle A=\pi-\dfrac{\pi}{2}-\dfrac{\pi}{5}=\dfrac{3\pi}{10}$ Let $h$ be the hypotenuse of the triangle. Use the sine trigonometric ratio of the angle marked as $\dfrac{\pi}{5}$ to obtain it: $\sin\dfrac{\pi}{5}=\dfrac{106}{h}$ $h=\dfrac{106}{\sin\dfrac{\pi}{5}}\approx180.34$ Use the Pythagorean Theorem to obtain the unknown cathetus $a$: $a=\sqrt{180.34^{2}-106^{2}}\approx145.9$
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