Trigonometry 7th Edition

Published by Cengage Learning
ISBN 10: 1111826854
ISBN 13: 978-1-11182-685-7

Chapter 7 - Section 7.2 - The Law of Cosines - 7.2 Problem Set - Page 378: 19

Answer

$b = 731 \hspace{1pt} m$ $A = 15.6^\circ$ $C = 12.9^\circ$

Work Step by Step

Using the law of Cosines: $$b^2 = a^2+c^2 -2ac \cos{B} \\ b^2 = (412)^2+(342)^2 - 2\times 412 \times 342 \cos{151.5^\circ} \\ b^2 = 534361$$ $$\therefore b = \boxed{731 \hspace{1pt} m}$$ Using the law of Sines: $$\dfrac{\sin{B}}{b} = \dfrac{\sin{A}}{a} = \dfrac{\sin{C}}{c}$$ $$\sin{A} = \dfrac{a\times \sin{B}}{b}= \dfrac{412 \times \sin{151.5^\circ}}{731} = 0.2689 $$ $$\therefore A = \boxed{15.6^\circ}$$ $$\sin{C} = \dfrac{c\times \sin{B}}{b}= \dfrac{342 \times \sin{151.5^\circ}}{731} = 0.2232$$ $$\therefore C = \boxed{12.9^\circ}$$
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