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 892: 11

Answer

See below

Work Step by Step

We are given $A,a,c$. Use law of cosines to find $a$: $$a^2=b^2+c^2-2bc\cos A\\b=\sqrt a^2+c^2-2ac\cos B\\b=\sqrt 8^2+6^2-2(8)(6)\cos 25^\circ\approx 3.6$$ Use law of sines to find: $\frac{\sin B}{b}=\frac{\sin C}{c}\\\sin C=\frac{\sin B}{b}\times c\\C=\arcsin(\frac{\sin B}{b}. c)\\C=\arcsin(\frac{\sin 25^\circ}{3.6}. 6)\approx50.8^\circ$ Since the sum of the triangle is $180^\circ$, we obtain: $$A+B+C=180^\circ\\C=180^\circ-A-B\\A=180^\circ -25^\circ - 44.7^\circ\\A\approx 110.3 ^\circ$$
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