Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 13, Trigonometric Ratios and Functions - 13.6 Apply the Law of Cosines - 13.6 Exercises - Skill Practice - Page 893: 38

Answer

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Work Step by Step

We are given $a, b, C$. Use law of cosines to find $c$: $$a^2=b^2+c^2-2bc\cos A\\ c=\sqrt a^2+b^2-2ab\cos C\\c \approx 19.3$$ Use law of sines to find: $\frac{\sin B}{b}=\frac{\sin C}{c}\\\sin B=\frac{\sin C}{c}\times b\\\arcsin (\sin B)=\arcsin (\frac{\sin C}{c}b)\\B=\arcsin(\frac{\sin C}{c}. b)\\B\approx 80.63^\circ$ Since the sum of the triangle is $180^\circ$, we obtain: $$A+B+C=180^\circ\\C=180^\circ-A-B\\C=180^\circ -80.63^\circ -65^\circ\\C=34.37^\circ$$
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